If you've ever needed your ACF choices to be dynamically generated by a SQL query, this plugin will help you get the job done.
You can mix and match static choices with dynamic, SQL-based choices by placing as many regular choices in the list as you'd like, followed by the special %%QUERY%% choice that will tell this plugin to load choices dynamically from the database.
An example on how to list users, setting the id as the value, would look like this:
%%QUERY%% : SELECT user_nicename AS text, id AS value FROM wp_users