This is a somewhat old thread...
Anyways, like some have mentioned topping is solely dependent on the user. If you feel that it adds in someway to the paint who am I to say it doesnt. I myself am a purest when it comes to LSP's and choose it for its characteristics. I am talking from a business stand point and not for personal vehicles. If a customer wants multiple lsp's on their cars, I'll give it to them but if they dont request anything specific I use what single LSP I feel will bring out the best of the cars paint. Natural gloss, bright shine, deeping/darkening, candy coating/plastic..etc.
Now with paint coatings like OG/OC, I feel it gives the paint a neutral gloss look so I can understand if people do top that with a wax or sealant purely for looks as the paint is already protected for years to come.
If you're a hobbyist and just getting into detailing then go for it! We all have the urge to try new products and combination with which we feel adds additional "zing" to the paint.