I know this is a somewhat “hotly” contested subject. This is just my experience with and without cooling fans under my refurb legacy Quad Wi-Fi (Ethernet cable connected) with internal 2Tb Seagate HD. Viewing via Nvidia Shield TV on a Panasonic TC58S1 plasma also using the app on my iPhone.
I put my Tablo into service on 7/11/26 and after almost 2 hours of updates I started using it immediately. For almost two months, I had to do soft resets, almost daily and a few times twice in the same day as I was constantly receiving the spinning wheel of eternal lockup and the error message “Playback Error”.
I started searching for posts that addressed this, but never found one that was pertaining to exactly what I was dealing with. I did see a few that talked about heat buildup, and issues with that, but within those I saw very mixed opinions. My unit was certainly quite warm to the touch. I measured the top of the unit in five places with a contact temperature probe. The temperature was ranging between 109° to 114°F.
I decided to try some cooling fans as I thought this would if anything help with longevity of the internal hard drive and the Tablo itself. Within a couple minutes of setting the Tablo on top of the fans set half speed I took the temps in the same 5 places and they ranged from 84° to 89°F. I decided to see how low I could turn the fan speed down before the temperature started to creep up and settled in at 1/4 on from the off position. When I place my hand on top of the unit, I can still feel air flowing up through it. I do have a magnetic filter on the underside of the fans. 
It’s been 3 weeks since I have been running the fans and I have only had to do a soft reset twice. This is a great improvement compared to what I was experiencing for the previous 2 months!
So take this for what it’s worth it’s just my experience.
Link to fans and controller: https://a.co/d/03lSMQyp
I’ve had usb fans on the Tablo (Orig Legacy 4) and HDD for years. Coincidentally a few weeks ago I disconnected them and have having errors. Guess I should plug them back in.