I rarely set out to do this intentionally, but I do end up doing it quite often. I'm a very slow smoker, and oftentimes have to put a bowl down simply because it's bedtime. I've not had a bowl turn bad from being allowed to sit overnight, though I suspect that wet aromatics might not react well to this treatment. I regularly leave everything from bright Virginias to heavy Latakia blends overnight with no ill effects.
Perhaps five years ago I was smoking a bowl of GLPease's Cairo one evening, and left it half finished when I went to bed. The next day I forgot the pipe and left for a two week business trip. When I returned, I found the pipe still sitting in the stand where I'd left it. I was sure that it was ruined, but curiosity got the best of me. I stirred up the ashes a bit and dumped them out (along with any dust that had settled), then lit up the pipe. It lit easily, and the rest of the bowl tasted fine. There was nothing magical about it, but there was absolutely nothing at all wrong with it either. I wouldn't hesitate to re-light an old bowl that I'd left laying around if I found one, though I don't think there's any "magic" to leaving a pipe lay around for weeks on end.
Most writings I've found on the "Delayed Gratification Technique" recommend dumping the ashes out when you put the pipe down. For no good reason, I always leave the ashes and dump them out before I re-light the pipe when I get back to it. I haven't a clue as to whether this makes a difference and whether the difference is good or bad. I do it from habit, and have not found any harm in doing things this way. (This did make dumping the dust out of my "long term experiment" a bit easier.)