In Diablo 3 for the PC, you start out with very limited storage space. Your personal inventory is decent sized, but your stash is pretty small, and costs a fortune to upgrade (or it seems like a fortune anyway at the beginning).
The nice thing about your stash though is that it’s shared among your different characters. Because of this, you can create characters that are simply pack mules to store stuff you don’t need immediately.
Now don’t get me wrong, it can be fairly time consuming switching back and forth from your characters to swap stuff, but if a friend gives you a mace that you can’t use for 20 more levels, do you really want it to take up your valuable space for that long? Probably not.
I still suggest upgrading your stash even when doing this method, since you’ll have more space to swap items and you won’t have to log in and out so much.