I think it's very regional. I work in various places around Yorkshire, so I'm not always on the same route, but it's generally 10-20 trains a week (mixed with other weeks where I can walk or cycle from home). Of a 20 train week, I'd expect 1-2 delays or cancellations every day. Unless we're starting or finishing early/late, I'd expect a seat once, in one direction only.

These are mostly 2 carriage Sprinters with hundreds of people trying to get on them. Sometimes I work in other places, and you've got these enormous 10 carriage long things that run North/South, but only 50 people trying to get on, so you always get a seat on them.