Normal maps, where should I use it?

I know a normal map is used to give a 3d model more detail than it really has. Useful for making detailed walls, bricks, rocks.

But is it ok for giving surface anatomy to a 3d model which would otherwise look very low polygone?

And if so, would it do anything for speed wise when running in the game engine?

My example, is making a detailed sculpted model, then taking the base mesh and baking the normal map onto it.

I guess thats what normal maps were invented for.
If you are not sure about the result it’s definitly worth checking out if it works for you.

Normal Maps shouldn’t slow down fps in a notciable way, at least not any different then any other textures.

Each face, edge, vertex has their own normals and base on those, normals for each displayed pixel are calulated. Normal maps don’t slow down computer as they just add to those existing already normlas deformation by RGB converted to XYZ so computer knows which direction light bounces off.
I hope this makes sens.