Do I need a french drain at sloped side yard?

I was digging at my sloped side yard along my house to get rid of the tree roots that might potentially damage the house foundation. After finishing the digging, I realize I effectively create a trench (1' x 1.5'). I can back fill the trench with dirt. Or I can take an advantage to install a french drain there. I never had water problem with my house. Do I really need to put a french drain at the sloped side yard? Or it's just a waste of time and effort to do so? I live in northern California where heavy rain only come several times a year.

 

I too would like to see what people think about these French drains as I have thought about putting one in but can't see that it wouldn't just
get clogged up after a few years but really have no idea.

 

I put in one French drain into a yard low spot. It was effective and lasted years. I presume it still works fine. My method was a bunch of 3/16 or 1/4 inch holes in 3 inch PVC, and having pea gravel above and below. Then topsoil and grass. If I were doing it today, I would lay some kind of barrier cloth over the top, because people usually recommend it. My motivation to do it when I did was that I was getting a concrete driveway put in, and ran un-drilled PVC below the driveway bed before the pour.

At the upstream end I put an elbow up, with a buried cap, in case I needed to clean it at some point. Never used the cleanout.