Speedcubing. It is very ignorant to claim that all you need is to know a bunch of algorithms. It is on par to claim that to win a basketball match you need to throw a ball into the basket. You need to think how to optimally solve the cross (or maybe to do extended cross), you need to be quick to spot the pieces for F2L and to choose optimal way to place them, you can choose different ways to solve the last layer to maybe gat an OLL or a PLL skip.
Of course. Games like go can help reduce the effects of Alzheimer[1]. I'm sure there are studies for chess too.
Sports are games with obvious health, mental and social benefits.
On a more intuitive level (aka I don't know if it's been researched), I would be surprised if most board games don't improve, at least a bit, the analytical thinking useful for many engineering fields (or even day to day life).
Challenges is a term too broad, you can imagine countless ones that have practical benefits. Learning-to-play-an-instrument-in-a-month challenge for example. 100 push-ups a day for a month. Read one book a month.
Depends upon what one considers practical? I had some nice (here: both informative and entertaining) conversations with someone I'd consider a genius, not via the more evidently practical skill of juggling, but because we'd made each others' acquaintance due to a mutual interest in Rubik's Cube.
If you haven’t seen it, you may be interested in https://youtube.com/watch?v=q6AsllXpKBU, which combines solving Rubik’s cube with juggling (1 minute, 41 seconds per cube)
