Do You Ever Use The 12V DC Connection On PoE Cameras?

Nope. Not sure why so many cameras still come with 12vdc connectors. It's just one more thing for the technicians to be annoyed about having to deal with. 

I do rarely in my lab for testing if the camera still works and someone has "misplaced" the POE injectors.  Or if the camera also has wireless communication I have used them because sometimes when it is just for temporary use finding an outlet beats running network cable.  I have even seen a few where it is used and connected to a light switch so that the executive and disable those cameras with the flip of a switch and be assured they are off.

Just for WiFi as you mention!

Also gone are the days of needing to go 24VAC to power the heater on exterior POE capable cameras.

Good riddance.

:)

Have a IR PTZ that requires 802.3.at or 50w AC PS.  PS blew and I didn’t have a hi-poe switch.

Did have a 40W AC PS, which worked until the IR came on.

The camera works with a regular 802.3 af switch and the PS together, though.

I guess that’s kinda of a “special circumstance” though, so never mind.

never once

We have when installing in elevators or other locations where we only had power and was using SD card for retention.

Have deployed stand alone cameras in hidden spaces using onboard storage and local 12 VDC battery on occasion. 

Using local 12v + SIM card keeps recording even if network cable cut/NVR tampered with.

With some of the Uniview cameras, you can actually turn that 12v input into a 12v output via the webpage when powered via PoE.
Very handy when you need to run a microphone or strobe etc...

I too have been thankful for the 12VDC connection when the PoE component of the camera failed in some old Vivoteks and I could use the 12V connection rather than installing a new camera.

I have seen it used as a backup in case the switch runs out of power, or to keep SD card recording operating in case of a network/switch issue.

I have used it for interview rooms to be able to easily toggle power to the camera on/off.

I have seen it used with solar, etc. or in standalone situations where there isn't a PoE infrastructure and they need to power 1 camera, so there is no need to put in  a new switch, or long cable runs, such as  a parking lot light pole or warehouse where they run liber and 24v AC.

Generally, IMHO the lower cost cameras have PoE only. The better ones have 12v and the best ones have 12v DC/24v AC dual inputs.

Yes, when the cable run is longer than 300 feet and has to go through a converter. 

We almost never use 12VDC, however we do still use 24VAC for outdoor environmental PTZs that are rated to draw 60+ watts when the heater/blower kicks on. Yes, there are PoE options even for that high a power draw but rather than rewire our roof, we found it easier to use EoC or EoUTP signal transport (depending on how the analog signal was transported) and reuse the original 24VAC when we replaced our Pelco Spectra IV analog PTZs with IP.