You free up a spell slot

You are describing function of this added feature ... wich should be obvious btw ...
Im asking about the spell.
I mean ... am i the only one who feels its a little strange?
Like "hey, you just decided to be a Druid ... goood, now let me teach you *a spell* that will cost you spellslots, and will take place in your prepared spells, wich will do litteraly exactly the same thing you can do naturally for free and without caring about litteraly any other rule apply to this spell" ...
My question is: Why would any Druid learn that?
