I just upgraded to BIAB 2021 (from 2016) and noticed the unchecked box for "Print to PDF" during the installation. I considered checking this but decided not to since it wasn't a default.

I would like to send chordsheets/notation of my compositions as email attachments to colleagues. Do I need to go back and install this in order to do that? Is there a reason why this was not a default?

Why is it not a default? I can speculate. PG Music started offering this utility several years ago, perhaps just after version 2016 (not sure). If you have installed it once, you don't need to install it again each year.

Long before PG Music offered this free bundled handy utility, I was using another one called Cute PDF and I still use it. There are many of these drivers available; some free, and some at a modest cost. All function as an alternate printer driver, so they really have nothing at all to do with BIAB or RealBand. You can use the PDF printer driver of your choice on any program that prints. PDF995 is a good choice among many.

Does that help?

But if I don't need to print out PDFs, but rather just save BIAB chordsheets/notation as files to send out as attachments, do I need to install a PDF driver (as you have to in Finale, for instance) or will BIAB handle that without the PDF thing?

You do not have to install any PDF printer driver to use BIAB or RB.

Window 10 includes a print to pdf driver.

If your computer is running Windows 10 just select the print to pdf printer option.