1s are throw-away, 2s are nearly so. You get four 3s and you've covered your 1s, four sixes and you've covered your 2s. That gives you leeway to shoot big on 4 of a kind, large straight, small straight, and Yahtzee.
I save my 1's for when I don't get my large straight after already claiming my small straight. The only time I ever go out of my way to score 4 or a kind is if I hit 29 (four 6s, one 5). I typically save it for last as a throw away.
