Links and lj-cuts both get read or not depending on a combination of poster, description, and how much tie I have/how bored I'm feeling. The second is probaby the most iportant for lj-cuts (I'll almost always folow the cut to anything that sounds at all interesting) whereas the third is the most important for links.

I use lj-cut for large images, many images, memes, anything NSFW, spoilers, possible triggers, possible TMI, very long entries, anything where I want people to read a disclaimer before reading the actual entry.