^^^briefly, there are some documented instances of the lock self-engaging on recoil. My own view is that this is a rare occurrence, but once would clearly be way more than enough. Some people don't care; I don't own any S&Ws with locks.
S&W has been quietly selling a lot of 442s without the lock, ever since a large PD declined to authorize 442s with the lock for their officers. I've bought 3 to date from my LGS, and I have no special in with S&W.
JMO.
ETA: so far as I am aware, there is no other difference, besides the added complexity and slight possible risk of failure.