Mary, as far as I know "snap" is just an entry setting on Cakewalk, a little like a "snap to grid" idea with some graphic programs. The size of this "grid" is set by (I think - can't be bothered to look now) what I think is the "res" setting - the one where you have a drop down list of note lengths. In most cases, if you have that set at 1/32 note, things will work out but on odd occasions you may need to alter a note length the way you describe.
If you want to stand any chance of a MIDI displaying on other systems without odd note lengths and positions occuring, I'd be very wary of positioning dots without "snap" and careful over changing lengths. You can make things sound "perfect" - the beauty of MIDI but in the process put a note lets say on 1.23 beats and make it a 1.7 note... Things impossible with notation.