I dislike the gameplay device of a set party limit.
This occurred constantly in Final Fantasy VII because the party limit was only three playable characters at a time, and there were a total of up to nine playable characters at a time. Party members were constantly asking, "Who are you going to take, Cloud?" and the party members' reactions to events would always be in the same format because the party members with Cloud would be optional.
Many games have sidestepped the gameplay notion of having all of your party members inaccessible to you by allowing you to switch party members in the middle of the battle. This is the way that it should be. If the gameplay system cannot handle more than three characters without presenting a problem in difficulty, then we should not be able to use more than three characters at all. It hurts the story when the developers have to make dialogue variations for each character that you possibly could have brought with you to possibly react to.