Instance limitations are limits on various aspects of instances (dungeons and raids) for various reasons like keeping a level of challenge, reducing load on instance servers, and slowing attempts to get rare drops. Some limit on how fast you can run through instances (dungeons and raids), primarily for farming or to get a rare drop. As expansions have been released and the level cap has been increased, the ease of soloing instances has increased and so players will often attempt to speed run through instances repeatedly.