I've competed in 1 meet, back in April.
Squats: I (and just about everyone) started warming up way too early, and spent about 45min repeating my last warm up every 10min. Went cold again at some point in there, had to redo my foam rolling. I think there was a misunderstanding about how long there would be between the girls finishing and the guys starting. Most of us in the first group of males started warming up at about 1:30pm, under the premise that we'd be starting at 2:00. I got my first two attempts (although the first one was wonky thanks to my dodgy warm up), but got stuck on the third attempt. Was quite disappointed with that, because based on gym lifts it looked like 150kg would be no big deal (in fact, early on in my training for this meet it looked like 160kg was going to be on the table).
Bench Press: Wasn't mentally prepared for the first lift; forgot that you have to wait for the start call. Brain was more aware on the second lift, which I got. I showed up planning to lift 100kg on my third attempt, but decided to play it safe and go for 97.5kg, which apparently was still over-zealous for the day. Like squats, my gym lifts indicated that 100kg would be realistic, so I was disappointed with that, too. On my second attempt (92.5kg), the pause on my chest felt way longer than it ought to, and it got to the point where, just before I got the press call, if I wasn't lying down with a weight on my chest I would have been throwing my hands in the air screaming: "The hell are you waiting for?!"
Deadlift: By the time these started, my care-factor was fairly low. If I wanted to test my maxes in the gym, I could go in, warm up and do it, and not spend an hour waiting around between events while the next group of lifters goes. It was sunset by the time I opened for deadlifts, so it would've been about 4 hours since I first started warming up for squats on the day. I made all three attempts. Based on how I went with squat and bench press, combined with how much zest I didn't have left, I knew that if I really had to grind it out the weight would be going back down again, so I opted for 177.5kg instead of 180kg, and the weight went up easier than I expected. I guess something went right in my training leading up to this.
Given how unsatisfied I was with my lifts, and that I didn't know the actual weights that anyone else in my weight class had used, I was more pleasantly confused than proud or excited when they put a gold medal around my neck at the end of the meet.
If there's one thing I learned about weight classes, it's that making weight isn't necessarily a good thing. Seeing as how 0ni can cut about 45kg of water, I figured "I'm right in the middle of the 74kg weight class, let's see if I can get down to 66kg and get a top 10 rank with PA." I weighed in at 67.5kg, and was significantly heavier about an hour later. There was only one guy in the 66kg weight class, I believe it was his first time competing as well, and he totalled 32.5kg more than me. You never know who you'll be competing against (at least in open comps), so fudging your weight might just put you against a stronger opponent. Besides that, your performance may suffer from worrying too much about making weight. I'm not sure if my failed lifts are attributable to that, so I'll stick with the more conservative stance that I simply wasn't strong enough this time around, but it certainly is a consideration.