IIRC, the good behavior clause was written to accomplish two related things. (1) Judges serve for life (2) as long as they behave.
It would have been a bad idea to merely state that judges have life terms without consideration of the possibility they could commit some act the congress found worthy of removal.
As for the practical difference between good behavior and high crimes/misdemeanors I’m at a loss.
I do know that if congress booted a couple federal judges each year, it would do wonders for our freedom.
Yes, I’ve also long thought our system would work better if perhaps every fifth President had been impeached and removed from office.
Would at least cut down on the nonsense about coequal branches of government.