Plus read-only isn't a guarantee. You can't write data, but you can run a bad select or join that ends up effectively locking the database.

SELECT * FROM my_200_GB_table will always be there.

Why should a select or join lock a database? Surely no database lets one query starve another of IO or CPU?

I like to suffix such account names with _readonly.

"find the login in your scripts"

It's actually quite nice using a database server that doesn't require explicit credentials to be used.