I hope it is good practice. When I was working through the Mesh Modeling Bootcamp, a few times I separated meshes where the instructor didn’t. My reason was that I was trying to get edge loops in all the right places to make editing easy. If everything is one large mesh, and different parts have different shapes, it’s easy to end up with a confusing mess of edge loops. If some object seems to have a few big parts (cubes for example), and they need to be modified a lot, it seems easier to me to separate them. For making a still image, it shouldn’t matter. You need to be careful with games and animation since it can have important effects. I hope some experts will comment.
