While the size isn't as important using dead shrimp because you can always put on more than one shrimp to cover a big hook, size is vital using live shrimp. This latter size usually is for sea trout in the Aberdeen wire style. Usually the smaller the hook, the better. The smaller, lighter hooks hamper the least the live shrimp's swimming ability. Naturally, if you're after bigger prizes, you have to sacrifice swimming ability for hooking power.
Dead shrimp are excellent bait for tipping all types of jigs.
However, often anglers use pieces that are too large. If you use a big chunk of shrimp, you may damage the action of the jig's skirt. One way to make certain the pieces aren't too large is to cut them with a knife, rather than pinching off chunks with your fingers. By cutting, you get a firmer shrimp chunk, and also you bait supply lasts longer. Another method of keeping the jig action while tipping with dead shrimp is to use a trailer hook.