When running more than one build on the same project, sometimes builds are waiting for others to complete before they complete themselves.

For e,g-
Starting build #1 and #2 on JobA on the same time (using NodeLabel plugin) but they are running on different slaves.
Let's say build #2 has finished its tasks, but is now waiting to build #1 with message:
Publish XML Summary Reports is waiting for a checkpoint on JobA #1.

When #1 will finish, just then #2 will also finish, even though it was idle and waiting for it.