I used FSD for about 99% of my 7674 mile road trip last month. It was especially helpful in navigating cities, although the main benefit was reducing fatigue on long driving days. Watching for the occasional mistake definitely kept me alert! It was a big help in driving strong crosswinds in the Plains.
As with others here, I was annoyed by the tendency to camp out in the passing lane. Also didn't like passing when nearing an exit. I found the acceleration and deceleration stronger than I would prefer; had it set in the middle between aggressive and chill. I sometimes overrode the hesitation at intersections on turns but, for the most part, it did surprisingly well.
One annoying thing was the inability to read certain speed limit signs. It nearly always ignored 65 mph if the previous sign was lower (TACC is the same, so not specific to FSD). That led to FSD trying to force me into the passing lane because I had my limit set so much higher than what it thought the speed limit was. Annoying.
It also wouldn't slow down much at times when the limit on two lane roads drops in towns. In New York state, it had a tendency to read highway signs as speed limit signs. I'd find the limit set to 20 mph at times on SH 20 or even 5 mph on SH 5! Had to scramble to dial the speed back up when that happened, or just accelerate myself.
So, some odd quirks but overall a big benefit on long trips. I will definitely buy it again for my next multi-thousand mile road trip at the end of this month. Doesn't really have much benefit for local driving here in the mountains, although it does pretty well on roads with no lines and dirt roads, to my surprise.