From what I understand, Iwo Jima was strategically not necessary and may have been a blunder of a choice with needless carnage.

"In his report to the secretary of the Navy, Adm. King maintained that Iwo Jima was the only island in the Bonins that "lends itself to the construction of airfields."
In the official Marine Corps history, Whitman S. Bartley carefully sidestepped this issue by stating that Iwo Jima "was the only island that could support a large number of fighter aircraft."
These statements failed to acknowledge that Iwo Jima was not the only island in the Bonins that provided landing facilities.
Both Chichi Jima and Haha Jima had sizable airfields already built " a fact that has not received enough historical scrutiny."