Most people lift at whatever speed feels natural, which usually means lowering the weight fairly quickly and using a bit of momentum to get through the lifting phase. Tempo training asks you to deliberately control that speed instead, often written as a sequence of numbers like 3-1-1-0, referring to the seconds spent lowering, pausing at the bottom, lifting, and pausing at the top.
The main thing slowing down does is increase how long your muscle is actually under tension during a set. A squat done with a controlled three-second lowering phase keeps your quads and glutes working through the entire range rather than letting gravity and momentum do part of the job for you. More time under tension per rep, especially on the lowering phase, has been linked to solid muscle growth, since that eccentric portion tends to create more of the muscle damage that drives adaptation.
Tempo work is also one of the better tools for cleaning up technique. Rushing through reps hides a lot of sloppy movement, a knee caving in slightly, a lower back rounding, a shoulder shrugging up. Slow the rep down and those issues become obvious immediately, both to you and to anyone watching. This makes tempo training genuinely useful when you're learning a new exercise or coming back to one after a layoff, since it forces you to actually feel each part of the movement rather than rushing to the next rep.
It's worth knowing that tempo training isn't really about lifting the heaviest weight you can. Because the set takes longer and the muscle spends more time working, you'll typically need to drop the load compared to your normal working weight for the same rep range. Trying to keep your usual weight while also slowing the tempo down is a common mistake that usually just breaks form. Treat tempo sets as a different tool with a different purpose, not a heavier version of your normal training.
A practical way to bring it into a program without overhauling everything is picking one or two exercises per session, usually compound lifts where you've got room to focus, and applying a slower eccentric while keeping the lifting phase closer to normal speed. Something like a 4-0-1-0 tempo on a bench press or a leg press is enough to notice a real difference without turning every set into a grinding ordeal.
Like most training tools, tempo work isn't something you need running all the time. A few weeks focused on it can genuinely sharpen technique and add a fresh stimulus after a stretch of normal-speed training, then it's fine to go back to a more natural tempo once the point's been made. Used occasionally rather than constantly, it's a solid way to squeeze more out of an exercise you already know well.