I read fanfic in installments because that's the way lots of writers post them, and I haven't got the patience to wait for the end.
I used to read a lot of books -- I'm a very fast reader. These days it's a more of a rare event. I hate being interrupted in the middle of a book -- when I get into a book, I'm totally immersed, and it's difficult for me to pull myself out far enough to do much of anything else. And with two small kids, I'm constantly being interrupted.
When I think I've got an opportunity, I'll make it a bit of an event. Somewhere along the way, I've gotten into the habit of eating while I read -- popcorn or crackers, something salty -- so I love to get my snack and drink, take my book to the living room, and lose myself for a few hours.
I also re-read favorite books, and while those can still enthrall me, it's a lot easier to read those in fits and spurts.
I guess that makes me a binge reader of books, and an installment reader of fanfic
PJ