I strongly considered the merits of .22 magnum shot when I got the 7-shot S&W 351c. Those extra 2 shots seemed like such a luxury, and I wondered, on a strictly STRATEGIC level, if having 1 or 2 chambers loaded with shotshells might be wise.
First, I believe I am more likely to draw on a snake or a dog than a human. If it's a snake or dog, I'd definitely want the birdshot. Yes, even for a charging Rotty. I don't wanna kill a dog, and if I could turn him away him with a loud bang and some stinging pellets, that would be better than putting a hollow point in him. The shotshell also gives me a much better chance of hitting him before he closes on me.
As for a human attacker, the CCI .22 mag shotshell patterns to about softball size at 12 feet. That's a lot of lead to the face! Even if each pellet is a tiny bee sting, catching a few dozen of them in the face would be disconcerting even if he wasn't blinded. Yes, a hollow point to the face might end the threat completely, but if it's a near miss, the shotshell would at least have some effect; the hollow point wouldn't. In fact, the hollow point could injure or kill an innocent. That's much less likely with the shotshell.
As for the LEGAL issue of using a shotshell in a defensive encounter, as noted above, the short-range and minimal penetration of the shotshell could help you completely AVOID a trial if a miss with a hollow point would have injured or killed an innocent, or damaged property. Then there's the argument you could make that the shotshell was an attempt to end the attack without killing the attacker, not much different than using pepper spray or a taser. You could also explain that the shotshell strategy was strictly because of its usefulness against wild or feral animals, and because you are statistically more likely to encounter an animal attack. Should be no different than carrying bear spray in a wilderness area and having to use it on a human attacker.
Still, the 351c stays loaded with 7 Speer Gold Dots, so you might say I haven't completely convinced myself of the above. I would load 2 or 3 shotshells if carrying in the swamps, though.