Yes , there is no hard rules, and the benefits of having the eyes closed depends a lot on the character !
To give a better example on where and why it was useful you can look here : Boon & Pimento : Cartoon series made with blender - #2 by 3dioot
Having the eye closed as default pose made a bit easier to get those poses.
In rig and eventually in animation.
The general rule is that we tend to rig with the mouth closed as it generally needs to deform a lot, therefore closed is simpler to work with.
For some cartoony characters the eyes might need to deform much more than a realistic or semi-realistic character, then having eyes closed might be a good option to consider.
And anyway, even if you don’t follow these rules you can manage something , it’s just a bit more convenient !