Do agencies really lose money to scope creep, or just complain about it?

I keep hearing the same story from friends running small web design, dev, and SEO agencies. A client emails something like "hey can you also add X" or "small tweak, shouldn't take long," and the team just does it, because pushing back over email feels awkward or not worth the friction. Multiply that by a year and it's apparently real money left on the table.

I'm trying to figure out if this is worth building into an actual product — something that reads your signed scope of work, watches new client emails (read-only, nothing sent automatically), and flags requests that fall outside the contract, with a suggested charge and a drafted change-order email you review before sending.

Before I put real time into this, I want to sanity check it with people who've actually run agencies or dealt with scope creep firsthand.

Is this a recurring, quantifiable cost for you, or something people grumble about without it ever really hitting the P&L? Would you pay monthly for a tool that reliably caught it, or would it just become one more dashboard to ignore? And is email even where most of this happens, or is the real leakage in Slack threads and verbal "sure, no problem" moments on calls?

Trying to work out if this solves a real painkiller-level problem before I commit to building it out. Would genuinely value hearing from anyone who's felt this firsthand.