Tar is a great tool for a squid, but I generally have a hard time finding a place for it among the other pilot tools I feel are essential. But when you can find a place for it and learn where to position for placing the tar, it can be an amazing tool. An absolute game changer against a lot of opponents.
Tar will mess up engines and guns quite a lot, and do minor damage to the hull and balloon. Enemies will eventually drift out of it, but if you play well you can keep them in the tar almost continually. With the negligible damage it does to the balloon, a lot of people will escape by going up or down to get out. In a squid, you can generally follow them pretty well and tar again, but I might recommend either a flamethrower or carronade as the rear weapon. A carronade will work against everyone, and if they're not chemical sprayed a flamethrower will let you really mess up their ship in a serious way. Even if they are chemical sprayed, the decent damage it does to the balloon and the fact that the engineers have to run around rebuilding and repairing everything increases the chance dramatically that they'll miss a chemical spray cycle. Mines also work on the back, but it's a little harder to aim those when you can't see them.