It alters the size of varchar & nvarchar datatypes - without using auto size, some are set to nvarchar(MAX) which will use a considerable amount of memory. Auto size will set them to minimum values of nvarchar(50) or to the current maximum length of data stored in the field, if greater than 50 characters. Safely Auto Size will set nvarchar to higher default value, there is a comparison I posted a while back here:
I’d suggest it straight away, there is no disadvantage from turning it on. I’d recommend “Safely Auto Size”. Without using this, the SQL Server memory usage for the SambaPOS DB is very inefficient and will use far more memory than necessary. So even from the start, turning on this feature should show a performance improvement.
On all the setups we do for customers, we have it turned on from the start.