It was probably there before Yosemite but you did not see it.
Usually when your Internet service provider requires it it will be used.
PPPoE stands for Point-to-Point Protocol over Ethernet. PPPoE has
become a favorite technology of broadband Internet service providers,
who use it to save time and money. DSL and cable modem subscribers, on
the other hand, have reason to be less enthusiastic about PPPoE.
PPPoE Client Overview
PPPoE combines two widely accepted standards, Ethernet and PPP, to
provide an authenticated method of assigning IP addresses to client
systems. PPPoE clients are typically personal computers connected to
an ISP over a remote broadband connection, such as DSL or cable
service. ISPs deploy PPPoE because it supports high-speed broadband
access using their existing remote access infrastructure and because
it is easier for customers to use.
PPPoE provides a standard method of employing the authentication
methods of the Point-to-Point Protocol (PPP) over an Ethernet network.
When used by ISPs, PPPoE allows authenticated assignment of IP
addresses. In this type of implementation, the PPPoE client and server
are interconnected by Layer 2 bridging protocols running over a DSL or
other broadband connection.
You can set up a new PPPoE or check the current set up.