Xbox games are getting bigger though, which require more storage, so by the time you've installed a few games and all the required updates and DLC, even a 1 TB drive might not last that long.
Bigger, yes, but even the biggest games only hit like 40 GB. That's like, the super-huge blockbuster sort of game.
So, that's 25 games right there you could fit, fully downloaded and installed, on ONE TB. IF you're sticking with buying literally nothing but the ultra-huge ones.
However, that's only the ultra-huge ones such as GTA 5. The average size of a game from a major publisher... AKA, a AAA game... is a bit less than 20 GB. In other words, most games have trouble pushing 20.
At 20 GB, that's 50 games that'll fit. This is providing that you buy from major publishers *only* (since indie stuff usually takes up very little space in comparison). Pricey games, then.
Unless you're buying games at a ridiculous rate like myself... are you going to hit that number anytime soon, starting now from 0? And consider how long it took to NOT yet fill the drive you already have. There's only even so many games on the XBone to begin with... looking it up, there's only 358 individual games on it, so that'd be a MASSIVE chunk of it's library. Actually, looking it up, if you were to buy literally every major game on the console... EVERYTHING that isnt indie... it would only total just over 3 TB. Fully installed. That's not me doing math to come up with that number, either. Went and looked it up, rather than doing the math and getting it horribly wrong (me and math dont mix well).
The total install size of every indie game put together, on the other hand, is only 440 GB.
So, If you were to have 4 TB available... that's literally the entire library of EVERYTHING on that console. AAA and indie. And you'd still have space left over. This should say something as to just how massive a terabyte actually is.
Now there's also DLC, but DLC is usually small enough to not really matter. The big publishers arent exactly keen on giving you lots of content for your money; there's a reason why everyone HATES DLC right now. Most DLC is made to be cheap to make, but expensive to sell... things like costumes and such take up so little space that it's almost unnoticable. There are times when it ISNT small, however.... if it isnt small, it's probably a Nasty Publisher Scam. AKA, one of those games (like SF5) where the publisher releases it in an unfinished form so they can sell you the missing bits later. In THAT case, you need the DLC *before* it'll come close to the usual size of a AAA game.
The big exception with those is DLC that acts as "expansions", however these are very rare and most games do not get one. Usually only multiplayer games, and only certain genres. In general, DLC is only going to take up a truly noticable amount of space if you're spending so much on it that it starts to become an actual problem.
So, considering aaaaaalllllllllll of that... one way or another, it adds up to the idea that, chances are, you wont be filling that already-huge drive you already have anytime soon, unless you plan on spending a rather massive amount of money on games within the next year.
EDIT: Anyway, I dont mean to rant at you. I just know how important money is in general... if I can save someone from spending a giant blob of it on something that'll just collect dust, it seems worth a bit of effort. I've made that mistake too many times myself in the past, after all...