qite so - its impossible and infact mostly undesireable to play with NO tension.
Playing with no tension is the only possible way to play efficiently and without destroying your pianist career quickly
I know this is just a matter of semantics but ALL misunderstandings depends on the limitation of language and wrong word use
What you're referring to is "contraction" NOT "tension"
Contraction is what give the "illusion" less weight and more weight because or more less inertia. It's impossible to contract efficiently if you're tensed
It's also impossible to play without contraction
But you're wrong about standing
Standing requires no kind of contraction whatsoever because the skeletal is self-supporting. This is very important because when we break the self-supporting skeletal alignment muscles conpensate by contracting
But the skeleton is self-supporting because the muscles must be free to contract for other tasks. When you break the skeletal alignment and conpensate with muscle contraction you'll always co-contract when doing whatever task
This is at the basis of almost all kind of tendon, ligaments and muscle injuries especially back pain, cervical pain, headcahe, low voice power and so on
The body is absolutey self-support and need no muscles to support itself, this leaves the muscles free to be used for all kind of activities and task. In order to contract a muscle must be "free" or "relaxed" ... because it's the only state that allows contraction as you can't contract an already contracted muscles
Tension is chronic long term co-contraction and is not relevant to body usage just to irreversible injuries