Think of it as a "VPN" packaging that get's wrapped around your Ethernet packages (except that in this case, it's a protocol that was designed for dial-up networking, and doesn't provide any P).
It's a way to leverage a lot of infrastructure that was originally in place for a different purpose (dial-up) with only minimal changes (requiring the client PC or router to be able to establish a PPPoE session, and tunnel it's outbound IP through that).
What's bad about it is that the terminus point at the service provider is a natural bottleneck for performance issues (unless you really trust the phone company to plan capacity for peak use, rather than somewhat more than average??) as it has to decapsulate all the IP packets for all the connected devices (think of it as a big Router at the telephone company that handles all the traffic for all the users on that "leg".) Secondly, the MTU is slightly smaller than Ethernet, which means that many/most Ethernet packets must be broken in 2 and then reassembled (ugh!) before retransmission, which adds more overhead.
All IMHO and YMMV, of course.