Scheme only allows internal defines at the start of a block, where they're all combined into a letrec (or at least treated the same way). A few do allow define anywhere; SRFI-245, which gives a formal description of the semantics, lists 5 implementations that do, including some popular ones, but it's hardly dozens.

Racket also allows it and encourages it in the style guide, using the "less nesting" (and thus shallower indentation ) rationale you bring up.

https://srfi.schemers.org/srfi-245/srfi-245.html