A quote tells you what something might cost. A fixed-scope contract tells you what it will cost, and what happens if either side wants to change the brief partway through.
The value isn't really about price — it's about the conversation you're not having six months into a build, when a change order shows up with no clear reference point for whether it's fair.
We write scope documents specifically so that any addition later has an obvious, agreed-upon baseline to compare against. That's the part that actually protects a client, not the number on the first page.