This has been a universal question of many artists from beginner to advanced. If you look back in art history, you can see detailed paintings of the old Masters, less detail in the impressionists and even less in a minimalist painting. Detail is up to the individual artist. How much detail do you like? Do you want to have some areas suggesting objects? Render all the detail? Or, have a painting more like a sketch?
To help you know how far you should go, make sure that you start with your statement in your painting. Make sure that you have communicated why you painted your subject. Have you said enough to clearly communicate to your audience what you intended to say? If you have, it may be time to stop. If not, what do you need to do more or change in your painting to get that across to the viewer.
In the featured painting, "Desert Rain", I wanted to get across to viewer the sense of being in the rain while viewing the desert. I love the contrast of light that will shine across parts of the desert while it is raining. In this painting, I moved the falling rain closer to the viewer.
I could have gone farther with the details, although that isn't something that appeals to me or is fun to paint. I painted enough to get across to the viewer what was happening, so that is as far as a went with the details. Try painting a scene with as little detail as possible to get across your idea. Is it enough details for your aesthetic senses?
Stop when you feel you got your idea across to the viewer, no more no less. It's your call.