Our accesses (both of them) are through the floor of our home.
It is annoying to have them come through the house, but I've only had technicians come do something in the crawl maybe 3 times in the 10 yrs we've lived here.

On the other hand, I don't have to worry as much about critters getting into my crawlspace through an access...

The inside access is probably also about 18x24"; so I am not sure there is much difference for size.

One disadvantage to having it inside--they are often in closets--that means that when I have to have someone go into my crawlspace, I have to clear off the floor of my pantry or guest closet... Hmmm.

kirkhall, that's exactly right. annoying and restricted space use

hmmm critters...can the door be sealed somehow temporarily.

Ours crawl space access is through a door in the powder room closet. The only time anyone has needed to gain access was during inspection at the time of purchase, eight years ago.

I've never had an exterior access door, but I think I prefer interior as having an outside door means another part of that house that has to be maintained against leaks, decay, etc.

I've seen them in the middle of a Walk-in closet floor--where it is less likely to be cluttered to begin with.

I do think they are fairly normal, especially as people are building crawlspaces differently now (sealed, etc).