I have done plenty over the years - From the West End to Tokyo and in between.
A lot of the time you could just be using headphones and no amp,
playing to clicks [from a couple a show to nearly the whole show]
Plenty of sight reading, but you can get a good run of rehearsals before preview night.
Like Doddy says, depping is down to the MD and fixers views on this. But it is usually ok and you would have a small pool of deps [MD/fixer approved]
Money is good and depending on the length of run will include holiday pay every 13 weeks.
Bigger shows have spin off's, like cast album CD's and DVD's to record [more money]
So in short if you are a full time player they are great gigs money wise.
You need to be all ears & eyes, and have good discipline and concentration levels.
It can become a bit of a bore, so its good to dep out for other gigs when you get the chance [and most do]
Garry