Verification is turned off by default for performance reasons. For most models, the extra error checking is overkill. For models where there is any sort of even marginally "questionable" geometry, you might consider turning it on. There are people who recommend having it on all the time, but I'm not one of them. I use it occasionally. Turn it on, ctrlQ, Tools>Check, turn it off. It can pack a 20% - 60% (approx) performance hit, which is why I like to work with it off, but making bad geometry also costs time, which is why I turn it on and use it now and then.
As for what entails "even marginally questionable geometry", I don't have a good definition, but definitely anything that has slivers, 2 or 3 sided patches, puckers, dark spots, missing faces, a lot of edges coming together at a single point, other features that fail randomly or for no apparent reason, etc are good candidates.
It seems to take a bigger toll on solids than on surfaces, and shells and fillets are said to be the biggest culprits.
There is a thread called "Verification on rebuild" from July 29 2005 where this was discussed in greater detail.
If you have problems before using Verification on Rebuild (VOB) then you will likely have more after turning VOB on. The other tool for checking the integrity of a part is the TOOLS/CHECK menu pick. Not everything reported by TOOLS/CHECK is fatal. Usually General Faults are fatal. Think of VOB as the smoke detector in your house. You won't have that annoying beeping with the smoke detectors off during a fire, but the end result of having them off will not be pleasant. Like a smoke detector, VOB can tell you about a problem before you get too far along.
If you are creating geometry that doesn't pass VOB or TOOLS/CHECK with the feature option, then you really want to find out how to create good geometry.
I am one of the guys who keeps it on all of the time. Mainly because my customers have me running around with my hair on fire most of the time and I don't have time to consider when it should be turned on and when it can be off. This also means that I don't have time to make a bunch of bad geometry because I had it off when it should have been on.
It extra important for a mold designer like me because bad geometry won't scale for shrinkage. Also myt customer like to `tweak'. Features don't up-date very well after changes with the sort of errors that can occur with it un-checked.
You have to decide what takes more time: SWx rebuilds, or having your guys go back and redo entire models because they are bad. I work with it on because most of my time is spent designing (thinking through stuff) not waiting for the computer to rebuild. It just sucks to lose half a day of work because there was a problem in the model that you didn't know about. Another risk to working with VOB off is that once a model is bad other features will have trouble merging with it. When this happens folks blame the new feature, not the real culprit because they don't know what the real culprit is! I saw a model from a customer where the guy worked for three months working around problems in the model that were caused by one of the first features - three months of wasted work that could have been avoided if he worked with verification on rebuild on. When I showed my guys verification on rebuild and let them make the choice, they all have decided to do the same. All it takes is losing two hours to an insrcutiable error to get a guy to convert.
I won't tell you how to work, but I urge you to at least consider turning it on and Ctrl+Q your models at least once a day. Of course, this takes time and runs a lot of risk in losing up to a day of work, but some guys think its more efficient than running with VOB on. Maybe corporate guys can absorb losing hours or days of work, but consultants like me have to make it right the first time because we eat the cost of our mistakes. If a rebuild goes long I can check my email or do some research - and remember, the extra rebuild time is a few seconds, so I was already looking at my email anyway and wouldn't notice it.
Ed, this doesn't happen much, but I've got to disagree with you here. This statement seems a little over blown. I've never had to redo an entire model because of having verification off. Usually, it's a single feature that has to get tweeked or created a different way. I don't typically get through an entire model without turning it on unless its pretty simple. I'm not suggesting working with it off all the time, just using it selectively.
Last week I was working with it on, just to see if I could get used to it, but I found I probably don't get as much email as you do.:-) My computer is only a single processor, but it has turned in the fastest times I've seen for some of the benchmarks posted to this ng. Anyway, with it on, SW still missed a bad solid face (created by cut with surface using a plane), which didn't manifest itself unil 15 features later, when a move face command created an invalid solid, and I had to go finding it manually.
Anyway, I'll stick with my earlier opinion that the importance of working with this on all the time is being overstated, partially since the errors are rare enough, partially because depending on what you're doing the performance hit is so large, and also now that it seems that it isn't 100% effective anyway.
There are many things like Verification on Rebuild (how'd it get dubbed voB, why not voR?) such as ctrlQ, several of the sketch settings and the various functions of the Alt key that SolidWorks for one reason or another doesn't do well at communicating. First, the software is too deep for new users to know everything. Third party consultants like me have a bonanza with obscure knowledge that people don't know, because seemingly complex problems are sometimes actually very easy to fix if you know the settings inside and out.
In terms of "discoverability", improved documentation would be most useful. I've been trying to push a "CAD Admin" training class for SolidWorks which would cover topics like this. A series of white papers written by experts in various types of design would be extremely helpful. There are a lot of things SW could do to get the word out and unleash more software power for more people. There are tons of very useful and at the same time underused functions in the softare.