If you ever see someone in T5 running through Airside looking like he's about to miss a flight, he probably is and he's probably me. Particularly work travel/travelling alone, I really leave it to the last last minute to get to the airport (unless it's been a tough day and I need a drink!).

Holiday time, I don't mind [departure time dependent], getting there earlier and having some food and drink in the lounge.

It's very much a horses for courses thing I feel...what you're comfortable with, checking bag or not, how much junk is in your hand luggage to sort through if stopped etc etc