A lot of comments here bemoan "Full Stack Engineers" as being Jacks of All Trades but Masters of None. But that misses the point. Don't forget that the full quote is:

“A jack of all trades is a master of none, but oftentimes better than a master of one.”

In a startup or smaller organisation an Engineer with a deep understanding of a single area (frontend, backend, devops etc) is far less valuable to the business than an Engineer with "T-shaped" skills (https://en.wikipedia.org/wiki/T-shaped_skills), a solid understanding of fundamental best practices and the ability to quickly understand new things as required.

This article nails it:

https://angel.co/blog/what-skeptics-get-wrong-about-full-sta...