You are actually supposed to treat your cuts with that on pressure treated. I never have. I thought about it, but could not find in store. Usually coat whole thing with color sealer anyway. As said above, there are always cuts you cant get to once assembled.
Make a plywood box large enough to hold one piece or more at a time and line it with plastic, then fill it with preservative, and let lumber soak some. Do all lumber and no more problems with rot or bugs.