createdb mydb -T template_postgis
-T template_postgis still necessary in new versions of PostGIS?
I never saw this db being different, it always has those 3 sql files you run there. Is this still necessary?
You no longer need to use the templates or even the script in the new versions of Postgis. As you can see in the Postgis - installation page, all you need is run the CREATE EXTENTION command.
I never use it, simply create a new DB from basic Postgresql template:
Then i load and run scripts postgis.sql and spatial_ref_sys.sql for your basic setup. I then use this template DB for all the others i create