What is the point to store variable before computation?

You only want to store a Variable if you later need to reference it. So if you aren’t going to use it? Don’t set it.
Also try setting Variables as Local Variables where possible in Functions to save unnecessary writes/reads.

However, if you find you have a snakes wedding on your blueprints and you can’t clean up with nodes, then setting a variable can help keep it neater but again, I always try not to where possible for optimisation.