I hate to say it but that is not true.
Ideally, the rear wheel needs to be on the ground (no stands) and you need to be sitting on the bike while checking the chain tension.
If you check it while it's on a rear stand, the tension will be too tight because when you set the bike back down, the weight of the bike will stretch on that chain just a touch. It's enough to matter, anyway.
Then, when you sit on it, it stretches it a touch more. Then, every time you hit a bump while riding, it "hits" even more tension on the chain.
Adjusting the chain tension while the bike is in the air is a key reason why chains get beat up before their time.
Again, rear wheel on the ground, you in the seat with your weight on the bike and verify the tension that way.
The only down side to this is that you do have to keep a closer eye on it but you were already doing that anyway, weren't you?
--Wag--