The thing is, the answer will depend so much on your dc's choice of university and choice of accommodation.
I can't really comment on any savings in energy as I've had 9 years of one returning home as the next one leaves, and when the eldest went, we weren't really monitoring energy so much. For us by the time they were in 6th form we weren't really paying out much for subs / lessons either so didn't save there.
Do notice the food bills go down though.
If you read all the hundreds of threads on here over the last few years and also have a look on WIWIKAU, you'll find what people pay out varies massively.
None of mine chose expensive Cities to live in.
They all also decided they would prefer self catered and all were happy not to have en-suites...... those 2 choices can save £100 per week, every week. That adds up.
We only gave them money from when they went in middle of Sept until the end of June. They all worked in the holidays not only for their own spending money then, but to save up for the next year.
Then, to some extent, it depends on the students' expectations of what they "must" have...... are meals out / take aways / coffees out a treat or a regular thing ? ..... do they think beauty treatments or gym memberships are a luxury or something they expect ? ditto new clothes, make up, going clubbing, going to concerts or festivals, other expensive hobbies ? Can they cook ? Do they understand that steak or fish is a darn sight more expensive than mince or sausages / that chicken breast is more expensive than thigh / that eating a vegetarian diet is cheaper again / that when you treat yourself that is fine, but you then balance that out with some jacket potato or eggs or beans on toast type meals / do they eat leftovers / do they understand about freezing food / about buying yellow sticker items / etc etc ?