Yes as you said, you do not need an all-in-one printer to send a FAX from your computer or cell phone or receive them for that matter. There are a number of services that provide this service, some of them for free, some with a paid subscription. For us, hooking the all-in-one printer to the “phone line” makes it work exactly the same as a normal FAX for sending and receiving along with being able to print and FAX documents from the computer.
The Keep It Simple Stupid principle works best for us in this case. If we want to send a FAX we generally print the document then FAX it. It is an extra step but we usually like having a hard copy in a physical file of the documents that we send to financial institutions, banks, and insurance companies anyway which are the only ones who we generally FAX to anyway.
Yep, what ever works. With the brother app on my phone, I can scan a doc over the wifi and then fax the scan or other files that reside on the phone. That’s pretty cool. Mostly I convert docs to .pdf and send via email or text these days though.