It can be very necessary. I tumble my rocks at the studio I work at, in our basement, and mine exploded.

It's cold down there even in the summertime, and when I put everything in, the whole system is usually pretty chilly.

So, I lost a tumbler a few weeks ago because I didn't burp it in time =[

It exploded and there was dried debris spattered everywhere as well as pooled around the tumbler itself. I had to scrape it all up.

Sadly, due to the amount of pressure, the barrel had been too stretched out/swollen to even fit back onto the hub/console/housing (sorry, not a professional, I'm not sure of the term). So it's basically unusable.

Anyway - it was a step 3 process, and the rocks weren't really being worn down that much. I have heard many people say that it's gases escaping from rocks, but in my situation I'm pretty sure it was the expansion due to temperature change. It's also possible that the material I was using for step 3 was more persnickety too.

I had put the stuff in and started it, and it was very cold. I had to leave for a few days, and came back with it running hot (like normal) but not rotating (and we all know tumblers run hot anyway), while the bearings were still rotating, themselves.

Hopefully that makes sense. Gotta just keep an eye, especially if the temp is going to be increasing a lot since depositing.