Quite often as a GM "the plot" as it were depends on the players getting to certain destinations. It's very much in the interest of "the plot" and the GM (if he has in mind what he wants to have happen next) to convey players to some destination with as few side treks and diversions as possible.
Oh you are so close to seeing it.
What if I as GM always time skipped to where I wanted the players to be but always played out in tedious and dangerous and unprofitable detail any travel to anywhere I didn't want them to be. This would be combining to different railroading techniques- hand waves and obdurium walls. Now, I'm not saying that this is good GMing, but it is a classic way to railroad while never saying "No" to the players.
Do you see how time skipping or hand waving away details that you'd normally deal with can be used to railroad players now?
And remember, if you are good at railroading players are choosing to go to a certain destination because you've dropped tons of rumors and hints and so forth into the scenario that steers players towards thinking, "That's where we are supposed to go." or "That's where we want to go." And so if they choose to go where you want them to go, then you make sure they get there as expediently as possible. "The road to Monomonomp proves to be safe and well maintained. After three days of fair weather you arrive at your destination."