If you never see the bits under the clothes and don't think you will see them in future use of the model then no there is no need to sculpt details other than practice. One exception I can think of is if the clothes are thin and you plan on have them be wet and cling to the body then maybe some details.
Great question, Lewis. It's evident that your head is in the right place with efficiency.
I tend to break down anatomy sculpting in 2 halves: "macro" anatomy which is like 75% of everything (musculature, bone structure). The remaining 25% is the "details", as I call them, which include pores, wrinkles, scars. So this exercise is that 75% to which I typically recommend to sculpt fully even if clothes will cover. In part because I often use cloth simulation to create clothing which needs a good mesh for collision.
The detail phase (last 25%) is usually where I will neglect areas that will never be seen. But each project can be different so there's not a hard and fast rule for all character applications.
