I'm used to seeing rough and ready shims under nuts. Sometimes they're a makeshift repair to get a player through a gig or recording session but I've even seen these on guitars that seem fresh from the factory.
Like this one.
The nut is sitting on a 'ledge' of sorts. I can see that there's lacquer over the binding and it seems the guitar left the factory like this. It's a bit strange. It looks like the bound fingerboard was machined down for the nut slot but something went awry.
Whatever the cause, it's not ideal. The best tone comes from good coupling of strings and guitar. Anywhere that a vibrating string can lose energy is a potential tone-suck. A nut sitting on a narrow ledge like this qualifies as something to address.
Out with the old nut and a little slot clean-up. Remove that precipice and cut a nice, new, bone nut.
Ahh, that's better.