It does not, for example, change when you may activate abilities that can be activated "only as a sorcery." The last ability cares only about the amount of mana that was actually spent to cast the spell, regardless of its mana cost
It also enables infinite mana combinations with cards like Freed from the Real
And dont forget that if the opponent is attacking your planeswalker, you can sacrifice that too
Sticky Fingers Sticky Fingers is the early curve enabler for aggressive red decks
Thats not to say you cant play any way to counter your opponents spells, but you need to run modal spells like Cryptic Command that can still be useful when cast during your upkeep a few turns later
While at first glance this looks like your average four mana clone, pretty interchangeable with any number of blue cards for EDH players who want this effect, it's actually a fair bit better than most