alt Hacker NewsIt depends on what your goals are. If you're doing it for fun or as a creative outlet this is great advice. If you're trying to actively get better you won't do it this way after a certain point. You need to be actively practicing and engaging your brain. It does matter what you play and how you play it.
Sure, there's "deliberate practice" and it matters - but so many people seem to think if they're playing that's what they should be doing, or it's a waste of time. In reality that often isn't much fun, and they start to associate the instrument with this sort of difficult and often disappointing experience, and they give up.