Aside from value as mentioned above, we want to weed out crap hands that might luckily hit the flop.
pairs 88+Yes, this is because you want to get maximum value. Doing this will build the pot, which is more profitable than limping in. Also, when holding high pocket pairs (Qs, Ks, As) calling and seeing the flop, the value of your hand can deteriorate. So, it's best to raise and 4-bet/5-bet all in when possible when holding these top tier hands.