I have a PoE+ switch (ZyXEL GS1100-8HP) that has a button on the front to toggle IEEE 802.3az compliance. I looked this up and found that it was a power management specification known as "Energy-Efficient Ethernet".
From the Wikipedia page, it seems that the primary effect is that the transmit path of the physical layer is put to sleep when idle. The user manual for the device says about the same thing.
Granted that for home use (the Wikipedia page mentions this and also it seems logical) savings are probably minimal. Also, at pretty much any given time something on my network is sending something -- a quick glance at Wireshark shows a typical stream of whatever; ARP, Dropbox stuff, SSDP, etc. and the activity lights on my switches confirm.
That said, I don't know why I would disable it. Without knowing more about it it seems benefits will be either zero or positive, i.e. it can't hurt.
So my question is: Why wouldn't I want to enable 802.3az? The fact that there's a toggle button on the front of this switch means that somebody somewhere seems to know that there's a reason to disable it; what is that reason?