Two things that I think he's talking about --

You don't want to force the shifter to try to pull the cable farther than the limit screw will allow. Say that, for whatever reason, the shifter wants to pull to the last click, but the limit screw is only letting it go halfway -- that's a lot of extra stress on the shifter. You probably won't break anything unless you're an idiot and keep trying to force it. Instead of using the shifter, then, pull on the exposed cable, like a drawing a bow & arrow, to move the FD.

At the other end, make sure the low limit screw is doing the work, not the cable. On my bike, I once figured out that the low limit was set so low that the cable was holding the FD in position instead. As the cable stretched (or the housing settled, or whatever people say), the FD would get a bit more out of position, and the indexing wouldn't work right. Now I always start FD adjustments with the cable detached.