You probably don't really care about your first few warmup sets. They are kind of boring, but you do them anyway because you vaguely remember tweaking your back that one time when you jumped straight into doing heavy deadlifts. So the lighter warmup sets are a necessary evil to quickly deal with, on your way to the fun zone. While this is understandable, a problem that arises is that many lifters under-appreciate their warmup sets to the extent that they don't really pay attention. They lie relaxed on the bench like a sack of potatoes while going through their light presses, or aimlessly bounce around in the bottom of their squats. And these habits set them up for poor performance and risk of injury later on. I'll explain.

Performance

Strength training is often thought of as growing and strengthening muscles, but this is only part of the story. Much of getting stronger, faster, or fitter, is actually a result of improved movement efficiency. When training, your nervous system continuously gets better at things like synchronizing the right muscle fibers for the job, or learning to relax the ones that are not needed for the moment. And you need to do many, many quality reps - insert 10.000 hour reference - in order to get this orchestra of muscles and nerves to work in unison. Not a single high performance body has been built without it.

Carelessly performing shitty warmup reps directly violates this idea of solidifying good technique. To stick with the orchestra analogy: only paying attention to technique during your heavy sets would be like having the conductor only show up for the actual live performances. It will suck. In a best case scenario your technical development will 'only' slow down, but more than often a few under-the-radar lazy habits and flaws are picked up. And these technical flaws will subsequently cause you to lose tension during the heavy sets later on, which will hurt performance. Maybe those empty bar lifts do influence our PR's, after all.

Injury

Now, regarding injury, let's briefly recall aforementioned trainee who is aimlessly bouncing around without any tension during his or her light squats. Many do luckily appreciate the vulnerability of the (lower) back structures, and as such try to lift with a neutral back position when lifting heavy. But back injuries don't only happen in moments of high stress. Even if you're only lifting an empty bar, or just 25% of your max, an unstabilized torso will ensure a tremendous increase of strain on the soft tissues of the lower back, which at the least challenges its resilience.

Of course the body - and back, in this case - is meant to move. But being loose during warmups and already tapping a few proverbial beers out of your back's vat of tissue resilience for a set that serves little function but to warm you up and get you into the technical groove? Sounds like unnecessary risk to me. Especially when considering that warmup sets easily amount for up to half of all sets performed in a training session.

So next time you get to it, get to it. I don't mean being a dick and leaving the gym in a misty cloud of chalk when there's no weight on the bar yet. But just pay attention. Visualize what a good rep would look like. Remember what your tension cues you'll need during the heavy sets, and practice them while you are not yet in the I-might-die-today intensity zones. Because it's hard to be conscious of technique when you are straining for your life. So practice that lifting setup even when the weight is light. Tuck your elbows. Spread the floor. Brace your core. Respect the empty bar.