if you are running long esters and only pinning m w f or something like that, then by all means only shoot glutes. there are proven scientific benefits to shooting glutes. however, if you are pinning ed or multiple times a day (when you add the gh in), then you may find you need to rotate (most definitely don't shoot the gh in your glutes lol). having said that, GH 15 says to only shoot in the glutes, even if it is ED (with the one exception of tren ace, where you can shoot in your delts with a 29 gauge 1/2 inch slin pin).