I'm a PM and I can code. You shouldn't let me near production code, but I think it's important for the PM to understand the technologies they are using in their products or advocating for/against. It makes PM's more credible with the engineering team, and it assures better understanding of the technology debates, and appreciation for when engineering pushes back. It's like an executive chef that just "creates" - what a bunch of bull - they should understand all facets of the experience - sourcing the ingredients, preparation, cooking, presentation, getting feedback - missing any of those pieces makes just makes you a less effective team player...