Why do people keep recommending Quicken Spell on every caster?

As the title says. Why do people keep recommending Quicken Spell on every caster?

I ask because I played a Human Sor for years and optimized my character as much as possible, even spending lots of IRL $ to get a +7 supreme tome. This Sor frequently ran out of or very low on mana. He rarely used Quicken Spell.

(To clarify, this is for a proposed Hardcore Blighter - 32 Point Buy Aasimar.)

Thankee!