I guess any knowledge is always better than no knowledge. But the difference in value between knowing the average slack in a schedule and not knowing it is probably as little as is imaginable. Why would you want to know this?

Let's imagine two scenarios, A and B:

In A, you have 200 acitivities of which 50 have zero slack and 150 have four days of slack each, for an average of three days of slack ([4 * 150] / 200) for all 200 activities.

In B, you have 200 acitivities of which 49 have zero slack, one has 600 days of slack and the other 150 have four days of slack each, for an average of five days of slack ({400 + [4 * 150]} / 200) for all 200 activities.

Is there really some significance to B having an average of twice as  slack? If so, I don't see it.

Interestingly, if it were critical path drag we were talking about, it might matter what the average drag of the critical path activities are. If we have 50 CP activities and they have a total drag of 500 days for an average drag ten days each, it tells me that somewhere there is still an opportunity to optimize (i.e., compress) the schedule, whereas if the total drag is just 100 days for an average of two days each, there may not be a great deal more to be wrung out of the schedule.

Fraternally in project management,

Steve the Bajan