Hard drive space is always an issue, even with a seemingly large capacity of 500GB being offered standard with each new console. Even if you don't opt to go full digital, you have to install every single disc-based game regardless.
Even then, the Xbox One has some advantages when it comes to expanding your hard drive capacity, since it enables you to simply plug in a high-capacity external drive, and simply start using it alongside the internal one. The PS4 on the other hand requires you to only use a 2.5in hard drive, and you have to replace your internal one to do so.
Nyko's just released Data Bank is taking things a bit further though. This attachment will allow you to use 3.5in internal HDDs as add-on storage for your Xbox One, which is great because those tend to be slightly faster, and also a bit cheaper than their 2.5in counterparts.
You can get your Data Bank at either Amazon or GameStop, selling for $39.99.
There is also a PS4 version which has been available since June.