Every time you walk up to the bar, it should be with the same attitude. It doesn't matter if it’s a warm up, or a max attempt. Part of “training” is also training the mental approach to you take with you to the bar. This also goes for taking a lift for granted.
I’ve seen plenty of guys struggle or even miss weights they considered “not worthy” because they did not respect it.
Your physical approach and mental approach to your work sets, gym sets, meet attempts, whatever should all mirror each other. Yes, I understand that lying down under an empty bar probably won’t require you to get AS focused as you need to be on a maximal attempt. However you should still be setting up the same way physically, as if it is. Lots of guys and gals coast through their warm ups, then change their technique and approach to the bar altogether once the bar is loaded.
Then, when the bar is nearing or at maximal weight, a completely new approach is taken, because the repetition of approaching the bar hasn't been reinforced.
Every approach to the bar should bring purpose with it. Why else are you even attempting it otherwise? Make your warm ups count both in terms of practicing technique, and in terms of mental approach, and mental cues.
People forget that the whole point of training, is essentially PRACTICE for competition. So if you don’t practice like you compete, then why do you expect success come competition time?
If your training builds confidence week after week, and you've been practicing perfectly, then come competition time, you’ll feel ready. You won’t second guess yourself, and you won’t need to manufacture confidence in order to fight off the demons of doubt. You will crush them under your feet on your way to the platform, where you will then conquer like a king who knows not defeat.