Can a Marathon Help an 800M/Miler?

In our recent discussions in the comment section of another post, the question came up "How does a marathon help an 800M/Miler?"  As B. Obama has stated, this is "above my pay grade" and I won't deign to answer definitively.  I will add, however, that I suspect the answer is "yes" it does, but  I'll let others chime in via the comments.

Coach Groves obviously thought so in 1978, as all those with their primary distance specialty being a mile or over had to run the entire Nittany Valley Track Club Marathon in February, just after the bulk of the indoor season was over.  The Half-Milers had to run 15 miles, which probably ticked them off enough as it was.

I think we had some pretty good performances from just about everybody after that, and I don't remember any serious injuries or illnesses from it.

Was Coach Groves Brilliant or a Dunce? (about the mandatory marathon only!)