Some sim time before getting airborne at £350 per hour is very sensible and a good way of practising hold entries, holds, instrument procedures, etc., especially if your real life experience is limited. However, I'd suggest 20 hours dual sim as a maximum. The sim and the aircraft feel different and I disagree with those who say "if you can fly the sim, you can fly the real thing". I progressed in a huge leap as soon as I got airborne.
Beware of schools who stick you back in the sim on days when the weather isn't flyable or the aircraft is tech - it'll cost you £50-£150 per hour for negligible benefit.
I used the sim solo just before the IR test to reinforce things like climb checks, cruise checks, setting the altimeter at the appropriate time, power settings, setting up navaids and radios, etc. - far more realistic than flying a route in an armchair at home.