According to Hornady, if you chamber it once in a semi auto rifle or pistol, the suggest you either shoot it or toss it. But they do make money off selling ammo....
I don't really clear my carryguns very often, but when I chamber I generally "ease" the round into the chamber for this very reason. I don't really see a reason to just drop the slide unless you have a legitimate need to be in a real hurry. No real need to do a press check either if you are watching or have a loaded chamber indicator. Of course you need to make damn sure the slide is fully into battery. Works for me, YMMV.
I periodically fire off the round I've been carrying in the chamber when I go to the range. Then I'll top off the mag again when I get back home.
If I've had to rechamber much, I'll use the first one out of the mag since it's been in and out of the chamber a bit two. This seems to avoid the set back problem for me.
As for the crimp on defensive ammo, it won't last forever. A friend was showing me his pistol one day and apparently, he'd been using the same magazine of Gold Dot .40 S&W for a few years. After years of loading and unloading the mag when going to the range and so on, they were pretty bad. I immediately told him to dispose of them and never fire them. Especially in a .40, they looked too dangerous to fire.
You would have to measure it before you chambered it for the first time and then you could always measure it just to see if it has gradually set back from repeated chamberings. Change the round if it shows movement.
I ran across this page on Dave Lauck's webpage, D&L Sports, about making ammunition more durable. I found the included post by John Farnam to be especially interesting.
When you load and unload the same round multiple times, at least two bad things are going to happen:
1) From repeated contact with the feed-ramp, rounds will eventually experience "bullet set-back." This phenomenon can usually be detected during close examination of the individual cartridge in question.
2) From repeated impacts with the bolt-face, the primer "pellet" within the primer-cup can fracture and subsequently become dislodged. Unlike the above, this phenomenon is not at all discernable via external inspection!
I always ease the round into the chamber instead of letting the slide chamber the round in hard. After about 2-3 rechamberings, I move the bullet to the bottom of the mag and keep track of the bullet order. This is good to do anyways because the round in the mag can also deform over time, especially the very top round touching the mag's feedlips. It's good to move them around a bit. Granted, it's going to take a loooooong time for this to happen, but it can happen. I usually fire off the rounds in the carry mag after about 6 months. About then, I'll usually have cycled the bullet order in the mag about 5-6 bullets by then.
I've re-chambered many rounds and have used them with no ill effects. The only round I've heard it being an issue with is .357sig. I can't tell you if it's fact or fiction, but I will know in the next year and I'll be sure to tell you then. LOL. As far as 9mm or .40sw goes, I can't see a difference with the naked eye.