How easily turn do statement scripts into stored procedures? Much modification is needed?
What is the advantage to do so?
Depends on the script but possibly a matter of copy-paste for the simplest.
Advantages: The script is on the server, can require permissions, has a name (I suppose a script file does too...). Easier to deal with input parameters. Fewer components involved. Usable by components that can't issue SQL directly - e.g., GraphQL mutations.
Disadvantages: Changing the script is now a formal migration for the database instead of an application update.