Usually that only works in Time-and-Material projects, and where management does a hard line with the original SOW, and the final delivery actually matches the original SOW.
When they don't, there are those hardliners that want a justification what they were paying for.
This is true. The three consulting companies/departments I have worked for have had T&M projects that are SOW based and staff augmentation projects.
I said in another reply (don’t remember whether it was to you or not) that I avoid staff augmentation projects for a lot of reasons.
But if you are in consulting and doing SoW based work, it’s a dereliction of duty by your tech lead not to insist on signed change order if the requirements veer materially from the SOW. It puts your company at risk of not being paid and/or having to do free work.
When they don't, there are those hardliners that want a justification what they were paying for.