Clinger stats are good for 0 cost, but they don’t hit particularly hard nor are they particularly tough to kill. Where they shine is to help with a Cave Goblin weakness: Cave Goblins require a lot of mobilility and the game only gives you 3 movements per turn. Clingers don’t need a movement action to reach places and they can reach places where it would be often not possible to in a standard move action.
Horde Clingers cheat the system in many ways, however, often it is hard to put the Clinger in a place that is really useful and generally in those situations it is a great time to Sly in Sneeks for a Clinger, so that next turn Sneeks can hit and then Sly away.
Clingers are the reason Cave Goblins should be very mindful of gate placement, as proper gate placement is necessary so that newly summoned Cave Goblin units can have a Clinger clung to them.
However, if those tricks are not enough, Cave Goblins have another way to help Clingers ...