I find the "rules are toys" framing of tabletop RPG design useful for several reasons:
The idea that system matters is reducible to recognising that toys have affordances; while there is of course no "wrong" way to play with a toy, no amount of open-mindedness will readily fit a bicycle through a basketball hoop.
It puts a line under one of the main objections to the "why not just freeform it?" thing; if folks are discussing how to make or modify a toy to achieve a particular set of affordances, blundering into the conversation going "why bother with toys when you can Use Your Imagination?" is unlikely to be well received!
Sometimes it's helpful to take a step back from a critique of a particular system and ask yourself: is this set of game mechanics really broken or incomplete, or have I mistaken a bicycle for a basketball?
