There are only a few private group study rooms in the library and when people wait inside them for hours "waiting" for their group, groups that are actually there lose out on the rooms, defeating the purpose. To make the rooms more accessible for everyone there should be mandatory rules of giving up the room to a group that is physically present when your group is not there after like 10 minutes. Just enforce the rules and update them to deal with the problem of room squatters.
From: undergraduate student

Pat Flanagan, Associate University Librarian for Public Services, replies....
Thank you for sending us this comment. We realize many students work in groups and that we don't have enough group rooms to accommodate them all. You have probably seen the signs posted beside the rooms, which state that they are for use by groups. We also have a more detailed policy on our Web site. Note that the full policy states that use of the rooms is meant to be limited to two hours, to allow more groups access to the spaces, and that no provision is offered for an individual to hold a room for an expected group. It also provides for use by individuals who may need a more private study area for some particular activity which requires it.

Staff may sometimes give an individual the benefit of the doubt and grant them just a few minutes for their group to arrive. However, library staff and security guards are available to you when you observe that group rooms are being used inappropriately. Don't hesitate to share your need for a room at the Ask Us desk or Circulation desk, or with library guards. Any of these staff will see that the policy of the
rooms is enforced.