Pros
Loads of opportunities to move about (though invariably forced, if you got restructured, which happened fairly regularly) Certain business areas / managers were more open to sideways moves than others - some business areas were quite 'if your face fits you'll do well'. Having a good line manager made a big difference to my enjoyment. I knew others with managers they didn't get on with who were miserable which is a big shame. Similarly if your manager didn't want to help you, or felt threatened by your ability, your progress could be stunted. But if you want variety, and responsibility without necessarily needing promotion to be satisfied, this can be a great company.
Cons
Sometimes trying to actually finish a project felt soul destroying because the company was so big that changes take time & if you are the sort of person who likes to see immediate results you might struggle as they can be slow to come. Getting anything at all done in the business feels like a huge achievement against the odds, and that's not necessarily because of negativity, more that the company is so big and has so many moving parts. I found the pay structures very opaque. Only by fluke did I find out that actually I'd been hired at the very top of a pay scale for a job band; this meant that when I tried for sideways moves in the same job band I was sometimes told I was too expensive for the role. But that is not transparent when the roles were so widely banded.