For other units, it still seems like a case of experimenting to see what benefits most from the additional health and fire support.
The once grounded unit will take off and attach to the unit permanently increasing its health and providing additional fire support, As mentioned above try doing this with the Hunter Captain and Goliath who can both have two Skitterers instead of one. Easily the most interesting and fun use of Skitterers, however, is making use of their unique new ability which when used can attach a Skitterer to any other unit.