Long story short, you are looking for mismatches and the flanker or Z position gives you that mismatch. It is another version of having OJ lined up on a safety in the Natty Title game. Getting man coverage with this matchup will make any QB salivate like Pavlov's dog and have Kiffin signaling TD on the snap!
Every play has a pre snap read. You are looking for hints in coverage and mismatches. Sending a man in motion is one way to forcing the D to tip their coverage, tight corners, deep safeties are others. If they are in regular personnel on D versus our normal 3 WR 1TE set, they will have to either drop a safety down or widen an OLB out to the Z. Oh the possibilities!!!
Crossing routes, corners, sluggo routes, option routes, will have these guys running loose in the secondary.