Why two new balls in One Day Internationals? Ground is getting smaller [true]. Bats are becoming powerful [true]. I don't seem to get the argument of two new balls helping the bowlers. Ideally, new balls are used by fast bowlers to good effect. Spinners can use the old ball to good effect too. Spinners can bowl with new ball [a different argument]. I want to know technically how will it help the bowlers?
White balls discolour more quickly, and so the ball was frequently being changed around 35 overs to allow the batsman to see it more clearly.
A new ball from either end (which is what happens) means each ball is only in play for 25 overs and so should remain in shape and white for the duration of the innings.
Technically it will help seamers and swing bowlers as a better ball is more useful to them. It will be of less assistance to spinners, especially those who need to grip the ball, but the slippery coating will normally wear off anyway, and most spinners playing ODI cricket are now used to bowling with balls that don't provide much assistance.