Basically it's like pests. If you find a spider, you use Raid. If you have a mouse, you use rat poison, traps or sticky paper. If you have rats (plural) you call pest control. And if you have cockroaches, you go to war, because everyone knows those things don't die easy! Only difference between physical pests and spiritual ones, is the spiritual ones don't die, but they can be repelled, stopped, pushed out, and tossed around. Afterward we put up protections to keep them from returning. They're not stupid, once they have been overpowered, they usually go away.
Thee are many many ways to get the same job done, but it's best to use the right action for the right situation. It depends on how you banish. If you use opposite forces (the being's weakness) to banish it, then yes, you would need to have an idea as to what it is to know what could counter it. Since most are malicious (when we decide to banish), positive, purifying energy isn't very pleasant to them. However most banishments are control -- pure force and willpower--therefore the only thing that must be considered is the strength of the spirit vs the strength of your ritual.
The other thing you must consider is if the spirit has attachements. If it has attached to a person, object, or location, then yes, banishment gets tricky. That's when exorcism comes into play, which is far more forceful and demanding than plain banishment.
Banishment is a kick in the backend and a door slam. Exorcism is holding up a shotgun with a big dog named Killer growling and snarling next to you.