Similar to using the handrail
When playing tennis, the other hand
Can serve as support
Or crutch
Think ideally
One *could* play using 1 hand only
But not firm, tightening up
But loose, yet controlled, well timed
Either way
Using 1 hand only
Is good practice
Especially for the weak hand
Then
Add the other hand back in
To support but not take away
The newly acquired independence