Is it better to wear tight or loose shoes?

For warming up on the wall, many climbers like wearing slightly looser shoes. This is to give their feet time to also warm up, but also to not have to warm up with the pressure from the tighter climbing shoes.

If you are climbing hard routes or projects, you will most likely benefit from tighter shoes that have little to no dead space in them.

If you are a beginner climber, it won't make much of a difference, and you should probably stick to slightly looser shoes. Tighter climbing shoes can provide extra performance advantages for climbers climbing difficult routes. If you are not climbing difficult routes, and you are a beginner, you most likely will not even notice these performance gains from the shoes, as the routes you are climbing do not even utilize their benefits.