Many writers work with first-person narration in their first books. It's way easier to get to know a character if you write them in first person (the "I" point of view). Third person (the "he" or "she" or "they" point of view) is tougher--it can feel more distant to you, the writer. Often to the reader as well, when you're learning. So opting for first person is a great way to get deeper into who this person is.
Of course, memoirs are almost always written in the first person. Why not? It's you who's telling the story, not a distant third person voice.
When you switch back in forth, there's an immediate hurdle for the reader. We go from close up to suddenly distant in voice. Like a camera focusing tight on something in the street, then zooming out at light speed to view the larger city. If you decide to switch, you need to be an awesome transition writer.
Here are a few books that use both first and third: The Lace Reader by Brunonia Barry, The Stone Diaries by Carol Shields, The Little Paris Bookshop by Nina George. There are others, but actually not that many. You can read what other writers think about this question here.
If you decide to explore this very interesting idea, be sure to check out books that already do it successfully. Study the transitions the author uses. How he or she moves from a section written in first person to one written in third person.
Your weekly writing exercise is to play with both voices in a current scene--find out which one works best for bringing your narrator to life on the page.