If I summon an elemental to help in a combat, once the combat is over the elemental just sits there doing nothing. When the party moves on, the elemental stays behind. When the party next gets into combat -- which could be a long time later and far away -- the elemental will appear in the party list and will have its turn during combat. Being so far away, the only thing it can do is move closer to the combat. Its got no chance of getting there before the combat is over, so it's a complete waste of time. Plus it's very silly too.
The elemental should automatically follow the party. Or failing that, have it unsummon itself after the combat it was summoned for.
I was looking for a comment about this (agree on all points, except that unsummoning bit, unless it worked to like Hunters mark and allowed you to redeploy the summon without wasting another spell slot).
The length of time a summon sticks around for will make them useful for multiple battles, but without the ability to follow your party, or be directly controllable by yourself (like when secondary characters join your group), they are pretty much useless.
Please give us direct control over the summons to move them around with the party!