Throwaway players in a trade shouldn't always be thrown away. I traded Housh and another guy for Welker and Ronnie Brown early last season, and I really only wanted Brown (there was someone I wanted off the WW more than Welker). I almost immediately threw Welker back into the free agent pool (this is before he became Brady's security blanket). Within two weeks, Welker was routinely putting up 100+ yd receiving games and Brown was on IR. I got unlucky with Brown, but I got arrogant with Welker. Sometimes the throwaway guy should be thrown away, but you need to put in the analysis on the guy before you dump him.
If you have a stud QB that rarely gets hit (Peyton, Brady, Brees), don't bother drafting a backup QB because the most likely scenario is that QB will sit on the bench every week except your starter's bye. There will be someone decent available that you can pick up as the season wears on to start that bye week. If your stud gets hurt, the guy that you drafted in the 11th round as a backup won't save your season anyway. Better to use that 11th round pick on a WR or RB that might break out.
RBs are a crapshoot, but the more shots you take, the more crap you hit. Most of my leagues have at least one bench spot for every starter. I am going to try to accumulate studs for the starting positions, get a kicker and defense in the last two rounds, get service-able backup WRs at some point, and get RBs with every other pick. So in a standard non-flex league (start 2 WRs), my roster going into the season would have be 4-5 WRs, 7-8 RBs, and 1 each at QB, TE, K, and DST. Some of those RBs will be dropped for bye week replacements as the season wears on, but some will find the starting lineup or the trading block, too.