Blizzard has been gradually increasing over time the cost of the shared stash in Diablo 3. So much so that it is a rather large gold sink for most players, especially low level ones. Here is an image of what the shared stash looks like when upgraded to full size, and I have highlighted in red/yellow the area you would see if you didn’t upgrade it below:
Shared Stash in Diablo 3
The highlighted four row area is entirely free and every player starts with it. This shared stash is a small chest in each major town that you visit, and basically it is storage space that all of your characters can access throughout the game (unlike in diablo 2 where every one of your characters could only see their own stash). Each character has a decent number of slots themselves, so I see no reason why you should purchase the shared stash beyond the first four rows as highlighted above. Blizzard has created some pretty heavy gold sinks for upgrading the shared stash, at the tune of 10,000 gold per 2 rows and 100,000 gold per tab (there are three tabs total)
You can have 10 character slots on your account, so why not start off using a few of the dormant ones as bank alts? A single character can hold almost as many items as an entire tab of your shared stash after all. Doing this will save you a lot of money, and early on in the game your character will need every gold piece he or she can find. You can also take the gold you saved not upgrading your shared stash and upgrade your artisans instead or craft the gear you need to progress in the game.
All in all, I think it is much wiser to save your gold, especially early on when it is a premium, and use “bank alts” to carry your excess loot. In the example image I showed you, that cost 30,000 gold to fill out the first tab. I have the gold to fill out the other two bank tabs, but what’s the point when I don’t even have enough gear/loot to fill the first one? You don’t need a lot of storage until you start playing multiple characters and at that point you will probably have plenty of gold to use expanding your storage space. Even if you’re a crafting fiend like me who makes a hundred thousand plus gold each night on the auction house, you don’t need a lot of storage since you can only post 10 auctions per auction house.
I could easily see players using their alts and naming them things like “MYGEMS” or “WEAPONS” and just storing gear and/or loot in their bags. After all, you can sell on the auction house from any character, and you can trade gear with the shared stash to get it from your farming character to your bank alts.