Marquis is correct. It takes me about 1.25h to get to central London. Allowing for frequent travel problems, actually finding the hotel etc., it's a 3h round trip, so for an hour's booking, that's 4h of my time - and you could knock an hour off either side in terms of doing in calls as well. So a 1h in call in central London effectively takes six hours out of my day, five at the very least.
Then there's the cost of travel, perhaps buying food and drink etc. as well.