Why do I want to adjust how many monsters I face in cata?¤When soloing or playing with 1-2 friends you could complete quests without having to nerf them, being a good reason to having to upgrade your gear..
¤When soloing, more abilities would become useful and not only powerstrike/cast , doublestrike/cast etc. Skills like Knockdown, Pillarcast, maybe even Multistrike and Crosstrike would be more useful.
¤Solo climbs would be a lot quicker since you could cut down your driving time with more than 50%
¤It would be easier for new players if they could choose to only face one evil presence instead of (up to) three
AND ¤Again it would be a reason for people to upgrade their gear in order to be able to kill more EPs thus increasing their chances to find better gear
Basically it would make it easier for new people, add a challenge to oldschool players, make soloing (or playing in smaller groups) more interesting and fun.
Downsides of this? I don't know, you tell me because I can honestly not see any.