Kodak gives very sensible instructions for small tank processing on their web site. It involves intermittent agitation that avoids bubbles in the developer. But, all water has dissolved air in it. And, bubbles arise from water exiting the tap into your sink. Watch for it on film when you wash the film. Tiny bubbles there with no agitation. The idea is to break up those bubbles by using agitation. At least that is one purpose of agitation.
While it isn't perfect, I usually use boiled water to get as much of that air out of the water as possible before I use it. I imagine it helps, but don't really know how to prove it. I know I don't get air bells on my negatives at all, even when I agitate as seldom as every 5 minutes.
"Often moments come looking for us". - Robert Frank
"Make good art!" - Neil Gaiman
"...the heart and mind are the true lens of the camera". - Yousuf Karsh