We are going to engage in a little anecdotal fallacy.. you boys ready?
I leave all of my magazines loaded all the time and have never had any trouble.
That first statement is complete bullshit. I have had all manner of trouble with my magazines, I've had them fail to feed due to dented bodies, bent feed lips, jammed followers and from being full of sand. That said I have never had one of my magazines fail to feed when it was in good condition only when something had obviously gone really wrong.
You'll see a lot of people saying a lot of things on the interwebz about keeping your magazines loaded, some say 'no worries,' others say 'don't' and yet some other folks say 'download a couple.' but who is right?
They are all right.. real pisser ain't it?
Lets look at this in a step by step, case by case basis.
If you leave your mags empty the spring is still under tension, don't argue, it is. While it isn't at its max compression it is still being compressed by the mag body so according to the 'leave them empty' crowd you still aren't cool.
If you leave it loaded the spring is compressed to the max putting tension and all that on the feed lips and spring. Not cool.
And if you download you're still under tension but less so..
Let's take a minute to flip the script, when you drive home and park the car you don't block up the frame to take the tension off of the springs so they don't take a set do you or have you ever heard of someone who blew a spring off their sweet ride while it was parked? Neither of those things happen because like a magazine spring the springs in your car is designed to do the job, they are designed to be under constant tension.
So with all that said I download my two EDC mags every month, to wash the sand out of them because that will cause them to fail.