I'll repeat what Gevonovich stated about having two blades a quarter open on the same spring. Not just long term but personally I make a conscious effort not to do that at all. It puts stress on both ends of the spring and can lead to breakage of the spring.
I know this because it happened to one of my scout knives when I opened two implements on the same spring to take pictures of the knife. Snapped the spring right in half as soon as I opened the second implement. All I wanted to do was take a picture and then close the blades. It's not common but it can happen and when it does it's too late to prevent it. Long term or not, I strongly advise against stressing both ends of the spring for any length of time.
I have some photos that were taken before I learned this lesson. I humbly admit that I still sometimes forget this lesson myself.
The first pic is the way I used to pose my knives for photos. The spring for the Spey and Coping blades is stressed at both ends.
This is how I do it now. Each spring is stressed at only one end.