Straight sets are the default most people learn first: pick an exercise, do a set, rest fully, do another set. Supersets flip that by pairing two exercises back to back with little or no rest in between, then resting once both are done. Neither approach is universally better. They just solve different problems depending on what you're training for and how much time you've got.

Straight sets tend to win when the goal is pure strength or lifting the heaviest weight you can on a given lift. Full rest between sets, usually two to four minutes on big compound movements, lets your nervous system and muscles recover enough to produce near-maximal force again. Rush that rest with a superset and your second heavy set on a squat or deadlift is going to suffer, which defeats the purpose if strength is the priority.

Supersets earn their place when you're training for muscle growth, general conditioning, or just trying to get more done in less time. Pairing two exercises that work different muscle groups, say a chest press with a row, means one muscle group is resting while the other works. You get more total volume done in the same session without needlessly padding out your rest periods.

There's also a fatigue and metabolic side to supersets worth mentioning. Keeping your heart rate up and moving between exercises adds a conditioning element that straight sets on their own don't really provide. That can be a genuine benefit if you're short on time and want strength work and some cardiovascular stimulus in one session, but it comes at a cost. Performance on the second exercise in a pair usually drops a bit compared to doing it fresh, so if that lift matters most to you, it shouldn't be the one tacked on at the end of a superset.

How you pair exercises changes the effect quite a bit. Antagonist pairs, like a bicep curl with a tricep pushdown, tend to let you keep decent performance on both since the muscles aren't competing for the same energy systems. Pairing two exercises for the same muscle group, like a leg press followed straight into leg extensions, is far more demanding and works well for finishing off a muscle group but isn't something you'd want to do on your main lifts.

In practice, most well-built programs use both. Straight sets for the first couple of heavy, technical lifts of the session when strength and quality reps matter most, then supersets for accessory work later on when the goal shifts to volume and time efficiency. If you're stuck for time and only have thirty or forty minutes, leaning more heavily on supersets is a completely reasonable trade-off. If you've got the time and strength is the priority, don't be afraid to rest properly between sets. The extra couple of minutes isn't wasted time, it's part of what lets you lift heavier.