Utilizing my bench properly is probably my weakest area in fantasy. I'm the type of guy who tends to draft the lineup he wants and only varies from it when forced to (injury, loss of job, or glaring matchup problems).
I can see where keeping a specialist guy (most likely an OF-SB guy) on the bench is going to be a big plus in a daily H2H league, where you can plug him in the second half of the week and have a good chance at taking a category for nothing.
In daily lineup leagues I can also see carrying an extra C so you can keep your counting stats up with all those extra days off.
Mostly though, I'm all about stashing potential closers. In a league with the positions you've listed I'm probably going to be carrying 4 starters and 5 relievers (hopefully 3 full-time closers and 2 in waiting). Depending on the starters I might even go as low as 3 starters and 6 relievers if I feel I can keep my innings up (not likely with only 5P spots though). In a more typical league, where you're starting up to 9 pitchers on top of your bench spots, I'll probably carry 7+ CL/MR and only 1 or 2 bench hitters, both of whom are probably hit-or-miss prospects as well.
In much deeper leagues where you're looking at 400+ players on rosters, instead of 200-300, I could see the value of insuring your team with more stable talent... but for a league this small I really don't see any value in holding a guy on your bench who's completely replaceable by a dozen guys on the WW.