The original intent for Docking (on Terriers anyway) was to enhance their movement in tight locations. Ferreting out varmints, and having to quickly move forward and back, to facillitate a capture and or kill.
There is/was a practical length of a Docked Tail, and that being short enough not to get in the way, but, long enough for their "handlers" to reach into a hole or somewhere, and pull them out by it. That length usually was between 3" and 4" for a mature Dog (sometimes a little longer).
I have one each...
My Make Sneakers is Docked... very cute !
My Female Becca has a full Tail... VERY beautiful !
Spccially when washed and fluffed.
But as stated, there's a time to do that, and it's when they are puppies, NOT adults !