It is in the best interest of your blackjack strategy to split a pair of 8s when you are dealt them.
There are two parts to a blackjack strategy, an offensive side geared towards lowering the house edge, and a defensive side to keep from losing too much in unfavorable situations.
Splitting 8s would be a part of the defensive part of your blackjack strategy.
If you do not split you are then playing with a hard 16—a stiff hand. Stiff hands are harder to play with because they have a better chance of busting than of hitting and staying below 21. In the case of stiff hands you are hoping that the dealer will bust.
But in the case of being dealt a pair of 8s, there is a way to turn what could most likely be a loss into a possible win. Your blackjack strategy in this case must be to split.
While it is true that you are betting more money because of splitting, you now have two hands to play, both of which start with an 8. You can think of this sort of strategy as giving your cards a second chance in this round. There now exists the possibility of winning one hand maybe two.
This is defensive blackjack strategy—utilizing playing options to turn unfavorable situations into situations in which you will lose less or improve your chances for that round.
You do not want to split every single pair that you are dealt, you do not want to split a pair of 5s or 10s for example. But should you ever be dealt a pair 0f 8s, remember to split them.