Stressed out

I read it somewhere last week but, of course, can't remember where now. The article said that plants (established ones, at least) should not be watered just because they wilt under the midday sun. Instead, you should stick with the '1-inch a week' rule unless your plants are drooping in the morning--after a cool night's rest. It also said that this stress would actually strengthen the plant. (I guess it's that old 'what doesn't kill you only makes you stronger' theory.)

Have you heard this before? Do you practice it?

I've always been told that stress weakens a plant and opens it up to all kinds of diseases and pests.

Now, I'm confused...