Why should I use the lens hood?

Is basic terms, when is the best situation to use my lens hood for my Nikkor 50mm f/1.8 G?

I leave mine on all the time on all my lenses

They prevent lens flare and ghosting which degrades the images you shoot

Is there a reason you don't want to use the lens hood?

A lens hood has numerous reasons to be used.

I have the same lens as you that I use for landscapes, as well as inside photography. That lens hood prevents light from coming in the sides which can cause flare in your pictures. Sometimes this can be a good thing, majority of the time it is a nuisance, if any light happens to bounce into the lens from the sides, the contrast and color in the image is significantly reduced. Another one, protect it from damage. It gives you an extra inch of plastic that prevents accidental pumps that could hit and scratch the glass of the lens.

Different hoods give you different effects, research on how the different hoods block light differently and find one that matches what you do.

Not to mention, they keep raindrops off your lens and also provide some protection from damage.

To prevent flare from light coming from the sides. If you don't have a lens hood, you can still avoid flare by looking for another angle.