Its more convenient if have this function because in some cases we dont want to print in A4 size, so if we setting to A6 size as for an example, the font become small and hard to read.
Increase font size
Make the font size adjustable

Font size is important not all invoices are sent via email some have to be printed and it is very small
Increase font size many customer can’t read invoices because font is too small
Increase font size, please. My customers can’t even read the bill, too small

Fonts are too small