Hi DaveBaker - and welcome. There are reasons for everything you do in wine making. So, if you heard that you should degas what is the rationale for doing that? Spoiler, here's the answer as I understand it: CO2 creates two conditions that you don't want when you are asking the yeast to actively transport sugar through their cell walls. The first is that CO2 raises the acidity of the solution as the CO2 converts to carbonic acid and too much acidity inhibits fermentation. Since honey has no chemical buffers to maintain pH you can find that any added acidity can make the pH drop to the floor and that can stall fermentation. The second reason is that the CO2 itself is absorbed by the liquid until the liquid is fully saturated with this gas. At that level of saturation the gas now exerts physical pressure on the yeast cells and those cells are then stressed by this physical assault. Stressed yeast returns the favor to you, the meadmaker by producing all kinds of compounds many of which taste bad. You want to reduce all the stresses on the yeast , not increase them. Okay,
If you look at the two reasons for degassing you will see that both reasons turn on the fact that the yeast is actively fermenting. Once you rack to the secondary you have determined - for all intents and purposes - that the yeast are no longer engaged in active fermentation so in the secondary there is no good reason to degas.
From the opposite point of view, might there be a good reason NOT to degas in the secondary? Well, if your technique of degassing is rather violent and you introduce O2 into the mead then there may be too few viable yeast cells after racking to glom onto that oxygen and so the O2 will bind with the mead. And allowing O2 to bind with your mead is called oxidation - not something that most mead makers work hard to produce... So, bottom line, no good reason to degas and good reason not to degas*. Should you degas in the secondary? You decide.
*If you allow your meads to age before bottling then the mead will naturally "degas" over time, but if you are bottling as soon as the mead clears you may find that the mead is still saturated with CO2 and that CO2 will end up in your bottles. If you cork bottles that are full of CO2, changes in air-pressure or temperature, and indeed, if particulates drop out of solution all this can cause the gas itself to drop out of solution and nucleate and this nucleation can provide the gas with enough energy to force out corks along with a column of liquid that rifles along the neck of the bottle... So before bottling you MAY want/need to further degas.
