Hey, semantics means meaning. You said you loosen them "a lot... until they're really loose" and only now you're saying "slightly loose." Hard to know what you mean or what you do when you have stated every type of looseness there is. 
The point remains: frequent loosening beyond making small intonation adjustments with strings at normal playing tension or just slightly loosened can cause premature wear on the strings. And excessive cycles of "really loose" loosening and retightening can result in kinks, flat spots or micro-cracks in the windings, especially near tuning posts and saddles - which can result in dead spots or even broken strings. And that's on top of elasticity loss from fatigue in the metal core/winding.
The point remains: frequent loosening beyond making small intonation adjustments with strings at normal playing tension or just slightly loosened can cause premature wear on the strings. And excessive cycles of "really loose" loosening and retightening can result in kinks, flat spots or micro-cracks in the windings, especially near tuning posts and saddles - which can result in dead spots or even broken strings. And that's on top of elasticity loss from fatigue in the metal core/winding.