All depends on your league settings. In most leagues you do not have to keep all or keepers or even any of them. It's how it setup after it that makes a difference. In our league we have 4 keepers, so if everyone kept four keepers then the first four rounds of the draft are just our keepers, so technically we don't start picking until the 5th round. If I kept no keepers, I would get a round 1,2,3 and 4 pick. If I was the only doing this, I would have 4 picks in a row before anyone else makes a pick.
If I kept only 2 keepers, round 1 and 2 would be occupied by the keepers and then I would have an pick in round 3 and 4. I hope that makes sense.
Some leagues in the above scenario the following is the way I understand it, Hopefully someone else can verify this, 2 of the keeper picks would be made up at the top of the draft and two at the bottom of the draft, which makes a difference.
10 team 4 keeper PPR league: (Starters in bold)
RB: A.Peterson. Sproles, Murray (flex), DeAngelo Williams
WR: Julio Jones, Cruz,Garcon, Jeffrey, Douglas, ROyal