He claims instability, but I haven't necessarily seen that. I typically avoid them just because it keeps the design intent clear and concise. I would claim that if you have a good use for them, go ahead.
As a SolidWorks instructor and long time abuser before instructing I agrre with Charles, it's not that it causes crashes or errors, it's that down the road if someone else has to modify the parts and has never used the selected contours they will have the stabibility problems in there own mind.....like WTH did that so-n-so do to make that feature..................!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
thats all all at the same time!
I tend to agree with Matt. I do a fair amount of surfacing and find that Trims are the most unstable features. I think a good part of that instability has to do with the fact that you have to select which bits to keep or throw away by picking in the graphics window. Sketch Countour suffers from the same necessity, so I shy away from it. Since I don't use it, I don't have any stories to tell about how it failed.
I also agree with Charles and Lenny that clarity of design intent is best served by separate sketches.
Wow, I agree with Matt, Charles and Lenny. Who'd have thunk?