[JonFish85]

In my experience, a good PM says "no" to things. I've worked on projects with a weak/ineffectual PM that suffer badly from "feature creep", because the engineers on the team continually moved to make "minor" changes to improve things that ultimately customers didn't want or need. To me, this is where a PM comes in to set the pace and keeps the engineers on track for specific goals.

Granted this is just my experience, and it's from an engineering POV.

[RougeFemme]

And, a good PM also says "no" or "can it wait" or "ok, if you insist, but here's the downside" to folks on the other side of the line - customers, senior management.

[jlees]

Yes, this. Dealing with the upstream is the part of product management that most engineers severely dislike. Also, dealing cross-functionally with all the parts of a product team that aren't engineering (are marketing up to date on the launch? what's our ops plan?) -- and reaching out across teams to collaborate and build new products. I've worked with some great tech leads who were almost entirely PMs in terms of what they did, but that left them with very little time to actually write code.