I always recline the seat briefly (and then, normally, immediately bring it back to vertical) when I first sit down, to check for a broken seat -- plus to have a definite answer that it isn't broken on the rare occasion you get someone intentionally blocking the recline (whether using a device or just their knees.)

I don't normally bring it down on the ground, although I have during extended ground delays. I've twice been caught on board a plane for hours during WX delays (once at SFO in AA domestic F, once in HKG in CX J) and being able to recline made a huge difference in my ability to sleep through them.

Having been in an flight with a mechanical failure that required an immediate go-around to the gate (although it was something where we could get back to a gate, and not an evacuation) I always wait for the 10,000 feet ding to recline and take my shoes off. I figure if something were to go wrong which would bring us back to the ground quickly (but in one piece) it would have happened by then.

The AA 738 F seats are a particularly nice implementation of this; the 738 Y seats do it too, a bit less nicely. The fairly recent, but now outgoing CX Y "shell" seats do, but rather badly (these have a different point of articulation.)