What is etc/mtree/NetBSD.dist for?

Can someone tell me what this file is for? The comment at the top of  
it just warns against editing it.

All I can see is that this file causes problems. Entries in it must  
be present on the system, so they can't be made conditional in the  
sets lists in distrib/sets/lists. This in turn leads to a whole lot  
of empty directories. e.g. When I compile with MKSHARE=no, I expect  
to not see anything in /usr/share. Instead I see lots of empty  
directories. There seem to ongoing problems where developers fail to  
keep the sets and NetBSD.dist in sync. Since each set has it's own  
mtree listing, I can't see an obvious use for NetBSD.dist.

IMHO This doesn't reflect the quality of engineering that NetBSD  
users aspire to.

Cheers,
Lloyd