I meant carving with complex shapes in my above post. I carve with boxes, but the problem with carving cylinders and arches and spikes and other shapes, is that it shatters the brush you are carving into, which gives you those misalignments, unnecessary faces/solids and invalid solids. It can save lots of time in situations where you need to make a small box in the wall, but can give you weird compile errors and invalid solids that may take longer to fix than to just do everything manually.
make a cylinder, lay it into a vertical brush, and carve, there you go. an arch (just clean up any misalignments with vertex manip, if there are any at all...)
Umm, why not just VM in the first place and not have to worry about misalignments later, as they are annoying to fix? Because carving with cylinders will
always cause a misalignment unless you have manually created the cylinder, and then it will probably happen too.