This is one of those things that's hard to measure.

Quite often I'd have to sit thru meetings that 99% of the time I'm not needed but for one specific minute I keep someone else from making an expensive time wasting mistake. It can be very difficult to determine what you're actually needed for in IT/Operations stuff.

Someone who is neither contributing nor necessary to a meeting may still be required to attend the meeting. For example, a mandatory training meeting includes people who are being trained, who are in this category.

If the meeting fails to accomplish its objectives in 50 minutes, then participants may excuse themselves with a clear conscience, but they may find themselves less-informed than coworkers who chose to stay for the entire session. Especially if there is "Q&A" for clarifications at the end of it.