All people have influence on your play experience; this is kind of the point.
This is true in the sense a butterfly in Mexico has an influence on Minnesotan weather. You can always find some link, some association of vaguely related events, but for the most part it's not true. I have been at many games over the years where most of the players had no influence on my play experience because of different spheres, different play times, or simply incompatible personalities that led to non-antagonistic but distant relationships.
That is why I specificed "... enough to be a detriment". There's a level of influence that matters and a level that does not.
As for becoming the problem, I don't think cliques are a problem. They're desirable. It's a game, it's my free time.. why wouldn't I want it spent on people I know are quality? I have no problems playing with the same people often, so long as I get along with them. The problem is when cliques take to social combat to diminish your experience.