I haven't done a lot of brake line work, but I have done it three or four times.

Basically, you can count on the rigid line nut to be frozen to the rigid line, requiring one to cut the rigid line and then remove the nut with a regular (tighter fitting) wrench. This can happen at both ends. The OP had asked about cutting the line and using a wrench - this is what people mean.

So, I also end up usually cutting the rigid line and using the flare nut wrench only for installing the new line.