Note: This is NOT a question about how to insulate the crawlspace mentioned
below. I already know what needs to be done there in the spring when I rip
out the floor.

Onward:
45 yr old ranch. The whole thing's over a full basement except for a 10x8
part of the kitchen that's over a crawlspace. Who knows why - maybe it made
the house cheaper to not extend the basement. Anyway, the only openings to
the crawlspace are two 8" x 24" rectangular cutouts in the wood supporting
the house. Just small enough to be useless. But, they're open to the
basement and cold air's pouring in.

Bought the place last September. It's well maintained, except I keep finding
little things that make me wonder why nobody dealt with them before. For
instance, there's no fiberglass batting stuck up between the rafters at
edges of the basement. What I'm wondering, though, is if there's a good
reason for those crawlspace gaps to be left open. Maybe to prevent moisture
buildup in the space? Peering in with a flashlight, I can see that there's
no plastic over the bare earth, no insulation of any kind (which is why I'll
be attacking it in the spring).

I'm not trying to heat the basement, but it can't be good for the house in
general to have that cold air coming in from the crawlspace. Any reason to
leave them open?