I have to agree with Wayne. In conceptual design, particularly, where you know you may come up with half a dozen possible ways to design something or some odd structure, I have always (regardless of CAD program, 2D or 3D) used "Save As" with a suffix, so I can always retreat to an older version.
I have frequently asked CAD software designers why they can NOT put in an option on the Save command which allows the user to "Automatically" save with suffixes, so a new file is created with each Save or each Save As in a trouble free manor. I know this can be done rather easily (not to say their are not file relationship issues to contend with).
It can save countless hours of time, when I reach a dead end, and realize I must retrace and redesign a complex part (or often parts) to a prior stage.
Bo