There's this idea in hypertrophy training that rest periods should be kept short to keep metabolic stress on the muscles high, and that this will be conducive to growth. Taking your example, suppose you want to focus on triceps. You could do benches to get both triceps and chest work, then superset with triceps extensions which isolate the triceps. The chest gets some rest between bench sets while the stress is kept high and recovery lower for the triceps. However, there's plenty of studies where all sorts of variables like numbers of sets, numbers of reps within sets and rest times are compared with regards to strength gains and hypertrophy. And it would seem that rest times don't have much of an impact. Far less than intensity and total volume, at any rate. Here's a meta-study looking at a variety of sources with that subject: http://www.ncbi.nlm.nih.gov/pubmed/25047853 (The effect of inter-set rest intervals on resistance exercise-induced muscle hypertrophy, Henselmans M, Schoenfeld BJ, Sports Med. 2014 Dec, 44(12):1635-43). It concludes that there's no evidence of shorter rest intervals providing superior muscle growth and in fact found one study where shorter rest had an adverse effect. The full text is behind a pay wall, but some conclusions (as well as other studies) are referenced here: http://strengtheory.com/hypertrophy-range-stats-adjustments/
Hard to say if supersets do in some other way increase metabolic stress or have other effects that would influence hypertrophy. With a lack of evidence of rest intervals being that important (and actually indications that more rest might be better, because it's likely more total volume can be accumulated), I can't think of anything that would make them superior to doing the exercises in sequence where the same muscle groups are concerned. Unless specific muscles catch a break on one exercise as in the bench/extension example (the chest).
I actually tend to use supersets for the exact opposite: to make better use of my time while letting muscle groups rest long enough between sets. To that end I superset antagonist muscles. For example, bench presses alternated with rows, or overhead presses with pull-ups. While resting from a set of one exercise, I do the other. Because the movements use complementary muscles the fatigue doesn't carry over much, meaning I get long rest times between sets while actually doing something in those. It can cut quite a bit of time from the workout total. It's also a small boost for burning energy when you're cutting because you're keeping the heart rate higher compared to complete rest.