[orclev]

> Lisp and related languages use Polish Notation everywhere.

> The main benefit is that (R)PN is parenthesis-free

... so what you're saying is Lisp has all those parenthesis just to troll us?

Seriously though, using PN can make implementing parsers a lot simpler as it makes the grammar less ambiguous.

[anaphor]

I don't know about less ambiguous, it can still require only single token lookahead and be context-free without any parentheses, but Lisp-ish languages are easier to parse because you have fewer productions to worry about compared to more complex languages.