Using a Raid/Large party group UI over 3 or 4 groups causes the game to lag significantly. The game will freeze briefly as you add members, and also on any status change just as zoning into dungeon or cave.
If you drop group or make smaller raids, limiting the size to 8 or 12 (maybe 16, although we had group members complaining it was starting) you can work around it. However with the limited amount of features to keep track of people (raid marker, etc) its difficult to keep those groups together.