Though if you're travelling for a meeting, you're genetally going to want to allow time anyway to make your booked train, in order to be at the meeting on time. Most peoples' trains are de-facto fixed in the morning anyway.
I'll want to allow time for the train to be late
Imagine a meeting at 1000 in London, meaning an 0930 arrival at the terminal at the latest. With a 2 hour trip and a 15 minute trip to the station that means an 0730 train and an 0715 departure from home.
So by leaving home at 0645, it means I can catch teh 0700 and arrive at 0900, with time for a coffee and croissant before the meeting
However
If the trip to the station is late, fine, I get the 0730 and skip the coffee
If the trip to the station is on time, but the train is late, fine, I get to the terminal at 0930 and skip the coffee
If I am fixed to the 0730 I have no buffer time for the train being late, and miss the coffee
If I am fixed to the 0700 I have no buffer time for the trip to the station being late
Thus I have to leave at 0615 instead of 0645. All because the rail industry likes to control people.
The only hairy time was when it got stuck behind a bin lorry in town!
Indeed, that's the whole point. Your taxi doesn't turn up, or your bus is stuck behind a lorry, and it's no longer a case of "oh well no coffee", it's "oh well no coffee and a new ticket anyway"