Since the vast majority of PC users still use the good 'ol DVD drive, the physical version of GTA V will be pretty hefty.
While a lot of PC gamers have made the jump to full-on digital distribution, there's still a large number who due to various reasons (collection, poor internet), cling to their physical boxed copies. The problem being that DVD is still the standard for PC, and while that was fine 10, or even five years ago, these days games are getting a little too big to cram onto the decades-old format.
By comparison, 2008's GTA IV shipped across just two discs, although it's 18 GB install size is quite paltry compared to GTA V's 65 GB. Whether you choose to buy the game digitally or physically, you better make some space on your hard drive for it to fit... especially you poor guys using SSDs.
Provided that there are no more additional delays, the long-awaited PC version of GTA V should be released on April 14 - over a full year since the game first launched on Xbox 360 and PS3. If you feel so inclined, you can go ahead and pre-load the game right now on Steam.