There are two reasons why you want to risk splitting the group to capture new tomeliths ASAP
1) Even if you only hold the node for a short time, you're gaining points during that time. If you capture a point and see an enemy army charging towards you and you need to abandon it, you still will have earned your team some points while preventing the other teams from gaining points.
2) Never underestimate the psychological impact of capping a node. Many players, when seeing a node on the map captured by an enemy GC will consider it a done deal, and not worth going after. An uncapped node will draw armies to it, and if you leave it be then you will have to fight tooth and nail to get it back. A capped node can sometimes be left completely undefended and no one will go after it because they've already considered that tomelith to be lost to them.