Learning parties or for people who are either brand new to a fight or people who have learned a smaller portion of a fight than would qualify for practice/Progression.
Practice/Progression parties are for people who have gotten down a portion of a fight and are looking to learn the parts after that point.
Clear parties are for people who believe that they have the ability to clear the fight in 1 or 2 tries.
Farm parties are for people who believe that they can consistently clear a fight multiple times in a row.

It is extremely irritating for the other people in the party when you clearly don't know the fight and try to sneak in. Don't do it. Totally back you up, OP.