I will cut to the chase, I am using both and here is why.
I have devices that do not have wireless connectivity which meant that wired connection is a must have. Instead of laying ethernet cables be it concealed or conduit, they are a mess that I simply do not want to consider. I could add wireless adapters for these devices but they are obviously not without cost. Also, instead of cramming all devices on the wireless medium, I could divert some to use HomePlug instead to spread the load.
Floor plan of a two-storey house:
The left side is the ground floor while the right side is the upper floor. The red dot in the living hall marks the spot where the router is situated. Ideally the router should be placed in the most central and open area to maximise reach.
Also, where possible and practical, devices that have Ethernet connectivity should be connected to the router without going through HomePlug.