Tolerance let's you function in world where people are not compatible to you. You probably know someone you can't stand but have to deal with them peacefully. It would be nice to live independently and filter out anything irritating, but as long as we have needs we have to rely on other people no matter how annoying they can be. It's why school nowadays force us into groups so we could build up that skill of dealing people we can't stand.

Maud Pie has a high tolerance because of her relationship to Pinkie Pie. Face it, if your sibling was equivalent to Pinkie Pie you would probably go nuts around her. That skill led Maud Pie to be able to tolerate every single one of the mane six, including the Alicorn of Friendship herself, and were no closer to establishing a strong bond. Twilight Sparkle even had to settle for a weak victory at the end of the episode.

Still there's a level of comfort of needing people beyond the interests between people. As you build your tolerance you can become more satisfied with life and eventually build up trust. For Maud Pie this shows for her love for Pinkie Pie which eventually extends to the rest of the mane six. Maybe someday I'll build an in depth analysis between Friendship and Tolerance but otherwise here is a picture of the rock pony herself.