If you don't have at least some ammo put away for a rainy day, when said day comes you may have one helluva time getting any.
I'm seeing this over and over: Someone has a gun, or several, but only had a box or two, or what was left of the last box they practiced with, of ammo. Crap happens, they decide "I really should get a couple of boxes", and there's little or none to be had.
I'm not suggesting having enough that you have to build a special storage building/area for it(though the idea is attractive), but have AT LEAST 500 rounds for each defensive weapon you own. You use some, replace it immediately. And if you live in a city/region that might have a high chance of 'civil unrest', for your primary defensive arm/arms a thousand would be much better.
Those aren't any kind of official numbers, just something that seems to me a good starting point. I've talked to too many people the last few months, especially the last 30 days or so, who'd had maybe two boxes for a fair while, realized they need more, and they can't get any.
As an aside: Someone tells you 'one box per cartridge per customer per day' and you want to argue, or think about that and say "Make it two", you're not getting two. And if you argue you're just going to piss people off.