Habitual association versus modularity

[Rifleman]

I'm sure no one doubts that there are advantages to each. At what level do we draw the line?

When I was active, brigades and above were considered modular. Battalions and below were really permanent teams, to the extent that a battalion commander would often get the same attachments each time a battalion combat team was formed.

Should this level change? Upward or downward?

Also, should we skip levels between habitual association at lower levels? For example: permanent platoons with permanent fire teams, but with the teams to be mixed and matched into modular squads? Or, permanent companies with permanent squads, but with the squads to be mixed and matched into modular platoons?

You get the picture. Where's the proper balance?