Watch the My Chick - Top Strings online guitar lesson by Matthieu Brandt from Guitar Lab: Triads and Hendrixian Double Stops
When you're moving to the top strings to play triads, you'll move into the pitch range of the singer or soloist. This means that you'll have to direct your attention towards the top notes of the shapes you play AND the rhythm you play your backup part in. These need to be adjusted to the singer or soloist' part. Rhythms might clash and the suggested melody within the triad progression might be in the way of the singer or soloist. Keep your ears open and blend in!
In a situation where you are the second guitar player or you're laying your backup parts on top of a piano or keyboard groove you'll have to reduce your harmonic imprint and be very aware of where you're going to fit in rhythmically. Triads on the top three strings can easily be derived from chord shapes you are already familiar with.