Resume writer here. Don't overdo the resume customization thing - I've had clients who wanted to spend lots of time tailoring each line of a resume to the job, and the time invested really isn't worth it. Especially if it becomes far too clear to the reader that you were essentially pandering.

For most people, different resumes for different roles (web dev, mobile dev, etc.) make sense, but if you have 20 resumes for different roles you're probably applying for jobs that you are highly unqualified for - nobody has expertise in so many areas where they need 20 resumes. 2-3 for most is probably plenty.

The key difference in most resume customizations is how you define yourself to the reader. I use summaries to tell the reader who I WANT them to think you are. If the job is "web developer", I want to tell the reader right away that you are a web developer right in the summary. You've defined yourself as what they are looking for, checked their first (and most important box), and they will now keep reading.

If that summary said "embedded developer", they may stop reading. If there was no summary and your first job title is "data analyst", they may stop reading.