They block
Cards that dont require additional mana, like Sigardas Splendor and Cosmos Elixir solve this, but ultimately are a touch unreliable, especially in light of other card draw options in white
I find that in the decks in which I run it, I mostly use it on instants and sorceries, since white does a pretty decent job of putting permanents back onto the battlefield with cards like Sun Titan and Emeria Shepherd
Picking up cards blindlyespecially Standard cardsjust because I might need it someday is a quick way to end up with a bunch of cards that are dropping in value quickly and dont have a deck
For example, we saw a cycle of non-Land permanents that could transform into Lands, such as Growing Rites of Itlimoc
Her ultimate isnt going to draw nearly as many cards as it would in her own dedicated green deck, but it might come in handy