Let's just use Perine ($4) as an example. Since my roster is at the bare bones 18, I can't trade him in for a kicker ($2 each) and defense ($2 each). If I do, my roster drops to 17, and is illegal. I would have to trade a $2 kicker or $2 defense for a $2 RB or $2 WR. The only $2 RB or $2 WR options are:
RB - Thomas Rawls (NYJ), Josh Adams (PHI), Deandre Washington (OAK), Ito Smith (ATL), and Travaris Cadet (BUF)
WR - Kenny Britt (NE), Amara Darboh (SEA), Equanimeous St. Brown (GB), Jeremy Kerley (BUF), Phillip Dorsett (NE), and DaeSean Hamilton (DEN)
Of the 11 players above, I would want their byes to not conflict my other starters at their respective positions - that leaves Rawls, Washington, Cadet, Darboh, and St. Brown. I will monitor these 5 throughout the preseason.
I would surely drop one of my 4 kickers over one of my 3 defenses. And the first kicker on the chopping block would be Aldrick Rosas, based mostly on bye week conflicts. Piniero and Parkey have no conflicts, and I think Fairbairn is undervalued.
If nothing else, I have to thank you for making me research these 11 guys. I usually don't dig that deep into my fantasy WR5, let alone a team's WR5.