The {{assettable}} tag includes the 'Properties' column which basically collects all fields from a specific asset type.
Some custom fields are used for internal reasons and are not only meaningless to customers but can even disclose unnecessary information and clutter the table.
If those custom fields could be 'Hidden from PDF' - the same way it is possible for ticket custom fields, ti would be a simple way to customise the table without hard-coding an alternate {{assettable}}