Hello TierraNicole9864
Here are three reasons cells undergo mitosis:
#1: To reproduce -- mitosis is the way that cells reproduce and create their own "offspring" in order to repopulate.
#2: To restore dying cells -- mitosis is the division of cells in order to create new ones, and to replace these cells that are fading away.
#3: To repair damaged cells -- cells divide themselves in order to help other cells that are not doing so well.
Mitosis is a very important procedure that happens very often in many living beings.
Hope This Helps!
-Chris