I think if you suffer with depression, or are at risk of suffering from depression, it's better to stay busy. Not stressful busy, but doing things... it can especially be things you enjoy!
When you sit around doing nothing much your mind can start to wander too much, I think that's when a lot of our harmful thoughts occur.
But if you are run down, then rest is also important. I think you can have a mix, though. For me the evenings are time to relax, sit and watch tv. In the day I don't keep busy but when I do my mood is so much higher!

I think though, you have to find what works best for you. And it doesn't hurt to try out each and see which one you prefer