How important are warm-ups? My opinion is quite different from most personal trainers out there, since I don’t consider them to be too important. However, this definitely depends on several factors, including your goals and circumstances.
Warming up is a general term for warming up your muscles to keep them warm instead of cold, which should prevent injuries and make you stronger. For someone living in a region with fairly cold climate, warming up before every session is probably the best idea, but as I live in California my body is pretty warm all the time.
I do a different kind of warm-up which suits me very well. For every exercise I am about to do, I simply start with lighter weights and a couple of reps, gradually working my way toward a goal for that session. The same goes for bodyweight exercises – I’ll do bodyweight pullups before I start my weighted pullups or a one arm pullup session.
You can also use various other activities as a warm-up. For example, what I sometimes do is mobility work which isn’t exactly a warm-up, but it can function as one. The point of mobility by itself is not to warm-up, but to gain and keep better mobility all around your body, depending on how you do it.
To sum it up, there are different reasons for warming up and you should find the one that suits you the best. For me, it’s just doing a couple reps of lighter exercise before moving to heavier stuff, but I train myself to be strong at all times so it’s definitely not for everyone.