As long as you're not carving with a non rectangular shape or carving into a non rectangular shape it should be okay, but you should learn to use the knife, slice and clip tools, and the best way to learn to use them is by starting with rectangles.
So in your case it's not that bad. Let me give you an instance where the carve tool will murder your awesome building.
Let's say I wanted to create the following wall (grey is solid, white is a hole):
Using the carve tool will result in this:
This is bad. Very bad. I can not stress how bad this is. If you ever need to stretch, rotate, scale or otherwise modify this series of brushes it will probably break. It is extremely likely that you will end up with microbrushes, brushes stuck inside of each other, etc. Torque is smart and knows how to deal with these but it's still not good practice. It will degrade performance and it makes your map much harder to manage when you're editing it.
This is what happens when cut out the shapes yourself using the clip (or equivelant) tool. It's only 1 extra step then the carve tool and only takes slightly longer, but it's a lot cleaner. Basically you just place 3 place holder pentagons where you want the holes to be (if you were a draftsman these would be similar to construction lines, let's just call them construction brushes). Then divide up the space intelligently so that each brush is convex (no indentations) but still forms the concave geometry (holes) you want.
