Boundaries as in - If someone asks for something that may not necessarily be in keeping with the music that
may "suit" the audience.
Having said that its very easy to judge a crowd and not get it 100% right. I did a 70th the other day and they just wanted chart music.
I dont think you can get it spot on for all of the guests - all the time especially in a wedding?
You can only keep a happy medium, unless some other form of goings on assists the situation (like a circle dance off) or it is "the anthem" for them.
Someone asking for dubstep at a Masonic dinner dance for example and is adamant that it will get everyone on the floor and will not give up until that track is played. you are then in the predicament of shrugging it off by promising to play it and not play it (in which case they will not have it), trying to explain that it may not work, refering to the party organiser, playing the track or perhaps saying no.
Dependent on the situation I would normally play the track and name the person who asked for it, assuming it is not completely out of "suit for the audience". Swearing and heavy music (skrillex etc.) would be a good example.