Ola Hallengrens code for Index Optimization - Clarifications
The difference between user_databases &amp; availability_group_databases is that when specifying user_databases you will optimize every user database (also the ones in the AG group) if you specify availability_group_databases you will only optimize the indexes of databases inside an availability group.

If you do not have tables with fragmentation above 1000 pages, this will not hurt your SQL Server performance. I recommend you also read this post from Brent Ozar. https://www.brentozar.com/archive/2012/08/sql-server-index-fragmentation/