My understanding is - and confirmed by ChatGPT- is when you use index hints in sql server or oracle, it skips the optimiser which would otherwise determine the index to use.
I have not looked into it for other databases.

One of my clients uses index hints on oracle for some 15 years now on a dataflex 600user system and it solved a lot of their performance issues in the early days. Now there is no incentive to let it go.

But it does increase the dependency on keeping the index. For the DF world not really an issue I think.