How Do You Know If Professional Editing Is Really Worth It

I’ve been exploring different book editing services, but I’m still unsure how to judge whether they truly add value or just polish the basics. What should authors realistically expect from a good editor structural guidance, style improvement, or full rewriting support? For those who’ve used professional editing before, did it significantly elevate your manuscript, or were the changes subtle? I’m trying to understand how to choose the right service without overspending or compromising the voice of the book.