I just learned something the hard way about AutoCat. This might be a bug or a feature I missed. Either way, if “description contains” is left blank and only $ amount has a value, this category will be applied to all blank rows all the way to the end of the Transactions sheet.
In my case I used category Auto & Gas and only filled in value $398 but nothing in the description column. I incorrectly though that it would find all transactions with $398 and apply Auto & Gas to them. It that actually but it continued down the sheet and filled Auto & Gas on all blank lines all the way down.