The phrase "for better and for worse" is mostly used in wedding vows. However, "for better or for worse" is more common. Use it to talk about something that has to happen, regardless of whether it will have good or bad effects.

For better or for worse, the newspaper industry is changing dramatically.

For better or for worse, we're being forced to cut our budget by 15% this year, and that's probably going to mean layoffs.

In reality, when someone says "for better or for worse..." it usually means that the situation is going to be worse, not better. :(