Mousemonkey :
Again I would have to ask "which ones?" I have been running an SLi rig since 2004 and in that time most AAA titles have supported SLi from launch, so what small time efforts that no one cares about are you referring to?
I have heard titanfall has problems with utilising sli capability, the witcher, also has bad sli support, also, you get micro stuttering with sli, something a single gpu does not, as well as that, a single gpu is more maintenance free whereas with sli you have to download the latest drivers in order for it to work, and, when new games are released, there is less hassle with single gpu owners having to wait for the latest drivers whereas if you sli, you may have to wait for the latest drivers in order for you to play the game properly, also, if the Op is building a new rig from scratch, then he will have to get a bigger PSU, and maybe have to spend more on a mobo that supports SLi
EDIT : EOS dosen't support sli very well either I think and also dark souls 2