Do they work? I've heard about it and that it supposedly helps you make gains faster. can someone shed some light on this?

Do they work? I've heard about it and that it supposedly helps you make gains faster. can someone shed some light on this?
Shortly, no...

But what kind of gains are you looking for? For muscle gains, they help by keeping constant tension on the muscle. For strength gains...no, unless it's a specific part. Example is lockouts for bench press.

They also cause lots of joint pains.

But I wouldn't do them.

that type of training is best utilized for different parts of a movement. for instance, strongmen can specifically train the bottom part of the bench press...or the top locking out portion if they feel they are weak in a specific area. you see people in the gym doing this all the time because they want to pile on as much weight as possible for their ego, sacrificing form and range of motion.

they work great if you're a bodybuilder. continue to do those after a normal set and it exhausts the muscles you just used even more, overloading the muscle for gains...but yeah, as for strength, it doesn't do much. more like a great stabilising exercise and bulk builder. and yes, i have also heard they cause joint probs.

what are partial reps?

what are partial reps?Not a complete rep. Examples are doing the first 5 inches off your chest on the bench press. This let's you keep constant tension on the chest and to get a bigger pump. This can also be used on the last 2-4 inches of the bench press called the "lockout"

They help powerlifters mainly if they have a stuck lockout on their bench press. If a powerlifter fully benches 600 lbs but gets stuck at the top on 650 lbs. They do lockouts in a power rack with 650-700+ pounds so it strengthens there lock strength, so they can fully bench 650 in competition. This is also used on deadlifts and squats as well.

This method can also be used for other exercises such as curls going from the top position and down halfway to keep constant tension.

They're used by both bodybuilders and powerlifters. For bodybuilders it keeps constant tension on the muscle getting bigger pumps, etc. And for powerlifters helps get past sticking point.

Who cares about "gains". This is a boxing board.