Getting your boarding card, and leaving your luggage before getting to the airport is great.
I've checked-in at Paddington Railway station (for the Heathrow Express), and left my luggage there, for flights to Riyadh and Madrid with BA, and recently my father with Finnair.
Dump your luggage, grab the boarding card and...RELAX. Get on the train, and arrive at the airport in 15mins. Bypass check-in, and smirk at the long queus!!
At Riyadh, you can check-in at the BA office down-town, and your luggage gets taken to the airport! It's brilliant, because check-in at Riyadh is chaotic; LH and AF use the same desks as BA, so the queus there are a nightmare.
Just thought I'd share that with you; I just hate all the waiting at the airports.