Update: I pruned my maple wrong for 6 years, a guy in Portland set me straight

Honestly I always cut my maple's branches right where they met the trunk, nice and flush, because I thought it looked cleaner. Last Saturday a retired arborist named Dale in Portland was walking by and asked if he could show me something on my tree. He pointed at the big swollen rings around my old cuts and said that's the tree trying to seal a wound I keep reopening, and that the branch collar should stay. He ran his hand along it and said cutting that off is like pulling a scab off every year. I counted 11 cuts on that tree with that same swollen look, going back about 6 years. Now I leave that little bump and my new cuts are healing way flatter. Anyone else get taught the flush cut thing by an old boss or neighbor?