There is nothing wrong with using sql logins, 99% of all web hosts will use sql logins not windows logins for database connection strings.
Web Platform Installer only works with sql authentication not windows.
If you install SQL Server using Platform Installer it will make it use mixed mode authentication (both windows and sql) but if you installed it separately it may default to windows only, but what you did is correct, you enabled mixed mode so it can use sql authentication. There is no reason to change it back.
Hope it helps,
Joe