I learned it in College doing diagrams it will do dimensionally accurate diagrams and it is VERY friendly to templates (Odds are i could find a milling machine and lathe template premade)
THe friendlyness to templates and to premade stencilled parts makes it a favorite of telecom and electronics for schematic and higher level diagram type stuff
but it can also do multiple colors and layers so that i could for example lay out a Milling machine or a table saw and make the Machine dimensionally good but also attach the WORK ENVELOPE to the stencil and turn it all into one group so stat if you move or rotate a tool the work envelope rotates with the Peice
SO with a milling machine the "Hand space" and travel room are accounted for int he shop design.
Or as a better example for woodworkers you could include the INFEED AND OTUFEED area required for a table saw (Which IMO is the tool with the WORST ratio of size of machine to space it ties up in usage)
I havent priced Visio since M$ bought it but it IS part of the OFFICE family now so the incremental cost of adding visio if you are an office user is likely small but i cant really speak for it
It's tough to beat a floor plan on graph paper and paper dolls of your equipment, at least for the early planning stages. Lest you think I'm a Luddite, I spend a significant part of my time running 3d parametric CAD software, but would still go the paper doll route for the preliminary layout.
I've always found expanded polystyrene sheet very useful in planning room layouts. Draw out the room size, and cut blocks to represent the units and stick 'em down with Prit Stick. Not only easy to move, but you get a 3D idea of what you are creating. You can even do walls as well so that shelving and windows are represented.
I just draw my shop to scale to fit on a sheet of paper (in my favorite drawing tool) and then similarly scale rectangular footprints of my machine tools, which I label. Then I can just move the little boxes around inside the big one until I get a layout I like.