We all have our drafting theories. The two prevailing theories to NFL drafting are: Needs-based drafting; and Best Player Available (BPA). However, too much deferential rigidity to either of those will leave you wanting. You need an approach that will incorporate the best of both. I believe the Impact Differential theory does just that.
Every theory is rooted in a core philosophy. My core philosophy is leverage. If you've been around GGN for a while, at some point you've probably heard this from me before, so I'll try to keep it brief. Basically, I believe that the teams with the most leverage win. Its not about having the least weaknesses or the most holes plugged. Its about having enough strength in a particular area (or maybe several) that allow you to dictate to your opponent the terms of the game. So I think you're draft should be geared towards creating leverage for your team.
The Needs-Based approach doesn't work because you're always chasing after holes to plug. The idea behind the Needs-Based theory is that you prioritize your draft order according to need. The biggest need in the first round and so on and so forth. The problem with drafting according to need is that it doesn't always allow for the better players to be chosen, and you wind up eventually diluting your talent base. Its better to be more strong than it is to be less weak. But strict BPA doesn't work either.
The idea behind BPA is to always grab the more talented player. But just because a guy is the best player available, it doesn't mean that he's better than the guy you already have. Seattle is probably not taking a QB in the first round this year no matter what their board says about who the BPA is. It won't help your team as much if the player you take is only a little bit better than the guy he'll be replacing. It probably would be better to take a guy that's a little lower on your board, but a lot better than the guy he'll be replacing. That is, you want to find highest impact differential possible.
The Impact Differential Theory isn't driven purely by need or strict BPA. The focus isn't even strictly a positional. The focus is about creating leverage. We could draft a WR in Round 1 this year, and it would be tough to find a WR in Round 2 that would create much of a differential from what was already on the roster; but the impact of adding another WR to the unit might outweigh the positional differential of adding a corner or a safety. Corner might be the biggest need AND the best player available, but the impact differential might make taking a tackle a more logical choice. Its not about getting better. Its about becoming formidable.