Do you cut inner corners? Of course, there will be a gap between the skirtings. For inner corners, you should use a butt joint, and if you have a profiled molding, you need to carve the end to match the profile of the other.
Protte
Who on earth carves every end when installing profiled molding? Seriously, is it common to do that today? I have trouble cutting the molding neatly at home; how could I possibly succeed in carving the end
Do you miter inside corners? Of course, there will be gaps between the baseboards.
For inside corners, you should do a butt joint; if you have a profiled list, you should carve the end so it fits against the other profile.
Protte
No, I don't recall writing that? It's usually only external corners that are mitered?