What's the point of the 4/8 person party buffs?

[Kurokikaze]

But with this buff implemented, a strong 3 or 7man group will be jeopardized not because they lack skill, but simply because they did not get that magical number of players in group.

I don't feel the need to impose players in getting a certain number of people just so they can get a special buff.

Either they give that buff to encourage the people to find an extra person or they make that encounter difficult enough that you need that extra person... ITS THE SAME THING.