I use it for my automated backend and I have to drop to a lower level command to force a tx when I have funds but they are unconfirmed and I need it to go out immediately. I actually wish sendtoaddress had a [minconf=1] option with a default of 1 that would allow finer control but it doesn't.
A couple of times I have resorted to doing a "getrawtransaction " then pasted the raw tx into
https://blockchain.info/pushtx (and that has actually worked).