I always try to cut lenghtwise and try to work out a border pattern so that can use lenght wise. There is much less stretch in the lenght of grain. When I use cross cut Salvage to salvage, the stretch always comes back to bother me... with wavy edges or it just does not want to lay flat against the other fabrics.
One exception is batiks there is almost no stretch on the cross cut or selvage to selvage.