The short answer
Virtual fax is the right answer for most businesses. It covers the real use case, which is sending and receiving documents. A few things are different: a physical fax machine you want to keep, an elevator line, an alarm line. Those belong on analog.
Keep the fax machine
A physical fax machine needs an analog line. It can run over the internet with an adapter, but the fax protocol does not tolerate the smallest hiccup, and the handshake fails. If you want a real machine on the desk, use a bundled analog line from your cable or internet provider. If you do not need the machine, virtual fax is more reliable than any fax machine you have owned.
Elevator phones
An elevator phone is a life-safety line. When someone is stuck and presses the button, the call has to complete without retries. Put it on analog: a line from the phone company or a bundled line from the cable provider. Most building codes and elevator service contracts require it anyway.
Alarm lines
Fire alarms, burglar alarms and medical alert systems dial a monitoring center the same way and expect the same kind of line. Leave them on analog. If your alarm company offers cellular or internet reporting, let them make that change on their own equipment.
Why bundled is cheaper
Cable and internet providers sell analog voice lines as add-ons for a small monthly fee, less than a phone system line plus an adapter, and it keeps the life-safety lines out of the business phone system, where they do not belong. We do not sell copper analog lines.