From what I remember from reading, burning
- increased growth of grasses in spring to feed native grazers
- encouraged fresh shoots from plants to grow long and straight which made them useful for basket material and arrows
- kept meadows open and barren of trees which encouraged grazing and made hunting easier
- captured and cooked insects such as grasshoppers for food
As California has suffered so much recently from wild fires, we're learning how seasonal burning was also import for preventing catastrophic fires.
Places like Yosemite were described by early white settlers as resembling a park, with large, spaced trees and grass beneath. You could see from one end of the valley floor to the other. With modern fire suppression, this is impossible, and many of the once vast meadows are now filling with encroaching pines.
This barely scratches the surface of how fire was used to manage land resources by California Indians. I highly recommend this book if you're interested in Native American practices, California history, land management, and native plants.