This quote for example: 'I’ve asked David Wong, working in the cryptocurrency team at Facebook, what would be the best way to be noticed by Facebook? He answered: “Side Projects” and “Blog”.'

To many people with kids, that reads: Facebook doesn't want to hire engineers with families, because the things they care about from folks are diametrically opposed, in many cases, to the time required with children.

I absolutely think that if you have the time and flexibility you should use it. But there are (and should be) other ways to stand out to companies or to create value that don't involve side gigs outside of the normal work day.

concerning professional advantages: after spending more than two decades writing software I seriously doubt that a side project gets you professional advantages.

Imho more important are soft skills that are not in the focus of most technically savvy people. Being able do communicate well and being a team player are at least as important in most cases- not everybody builds a new google...

We tend to focus on technical aspects while most fail to see that this is not a purpose in itself (in most cases / companies) but the purpose is to generate business value.