I'm putting this here because the reference is to a Sony ban of a user on Neogaf, but it would apply to Microsoft and Nintendo all the same. Hell to digital only non-media purchases in general (Amazon, iTunes, ect).
This guy was banned from PSN for violating their TOS, which in this particular case may or may not be BS, the reasons for his ban aren't really the point. The bigger point is that by being banned he not only lost the ability to play games online, but he cannot log-in into the servers in anyway. If his current PS3/PS4/Vita takes a dump he will not be able to log in to access his download list for games he has paid in full for. He is effectively locked out from purchases he's made.
I keep my digital purchases to a minimum. In the case of music and books thankfully it can all be reasonably backed up and in most cases doesn't have DRM (or the DRM is easy to remove). If iTunes or Amazon were to disable my account I don't think I'd lose a thing. PSN/XBL on the otherhand, there is no method of a "backup", you are wholly reliant in their servers authenticating and then permitting you access to goods you've purchased.
For those that are 100% digitally invested, you've already resigned your ability to lend, trade, resell, ect. Now consider that you yourself might lose your own access. I admit it's not something I really considered before see the gaf thread.
Also, don't use paypal on PSN. In the case linked above, the user believes that paypal initiated a charge-back with Sony on a purchase (maybe they thought it was suspicious) and charge backs must've been against Sony's terms of service. Not to defend Sony, it's ridiculous that they'd ban someone over it, but Paypal is notorious for how it is quick to chargeback.
For PSN it seems the safest route is just to buy Prepaid cards.