There are these features which arguably should be conditional, but are not:

* Unlock purchasing all 25 area tiles, when the last milestone is reached.
* Unlock the "Basic Road Created" milestone from the beginning.
* 100% refund from recently built roads at all difficulty levels.
* Steam achievements are enabled for all difficulty levels except Easy and Custom.

This is important because, for example, I prefer "unlock 25 tiles with right price" which increments the cost of the last tiles.