What are the differences between
You can use
exec_prepared to optimize SQL query, see documentation.
exec_params lets you execute specified SQL query with binded parameters.
exec_prepared lets you execute prepared (parsed, optimized etc) SQL query specified by its string identificator/name which you have got earlier.
If you make a lot of similar SQL select queries and difference is parameter values, you can make it effectively by preparing SQL statement once (you receive it identifier) and execute it with different parameters multiple times.