Usually I think they are reserved for special occasions but I have been seeing more ladies wearing them daily. Today I saw a lady with a ring similar to this one but center stone was much bigger, she said it was called the "Duchess" and I thought it was so beautiful and told her so.
I love them too. I think they emphasize the right hand gorgeously. I have changed my nail polish to match the ring. I love to wear them but a lot of times don't because I am always doing something around the house.
I always wear one of my large and heavy right hand rings (and sometimes on my left hand, instead of my wedding set) without regard to my clothing or destination. My rings are for ME! It and bracelets are my favorite since I can see and enjoy them all day long, not just when I pass a mirror. The only problem is not to get distracted while driving. If you love it, wear it.
And do not be shy to compliment a ring you like on someone. It might just make their day.
I say they are for casual and formal, but it depends on the style of the person and if they can carry it off. I've seen people wearing them at formal occasions and they looked ridiculous, but perfect on someone else wearing jeans....I think the era of "cocktail rings" for evening wear is being replaced by the era of "RHRs" which you can wear whenever it suits you.