Those of you who pre-purchase Titanfall on Xbox One, and presumably PC, will be able to pre-load the game ahead of its March 11 release. The ability to pre-download and install the game was confirmed from Respawn Entertainment co-founder Vince Zampella, but he never specified which platforms that applied to. However, on the game's product page on the Xbox One games store, it clearly states pre-loading will be available; although, it will not actually be playable until after 12:01am PST on its release date.
Here's Microsoft's official policy:
Pre-purchase: You will be charged the full price immediately for this pre-purchase. Xbox One game expected to release on March 11th, 2014. You may download the game from Xbox Live before then, but it will not be playable until after 12:01 AM PST on the release date in your country.
There's no mention of pre-loading for the PC version but it can be assumed that Origin will allow you to do something similar.
It was also revealed that Titanfall will require 15.88GB of space on your Xbox One. Don't be alarmed by the relatively small install size, though, as it's important to remember that Titanfall doesn't have a single player campaign.
A specific install size isn't revealed for PC though Origin mentions you must have "at least" 10GB of free space on your hard drive.