2kewl4u said:
Only because of #17's wish, if someone-else had made the wish who knew what could have happened?
Considering that all of the Universes would have been immediately destroyed weren't for Goku wanting to do the ToP, giving them a shot at surviving is still a far better thing than having them being destroyed immediately. It was risky, but it still gave them a chance to survive, so it wasn't a bad thing per se. The fight against Freeza was also something risky, letting the androids to be built was also something risky, allowing Vegeta to survive was also something risky... Goku believed he'd remain one step ahead, but still that wasn't a guarantee of the sort... Goku had to show confidence btw, otherwise Kuririn could just of kill Vegeta right there.
A technique that takes forever to charge. Goku could already sense Ki as-well, so hiding to charge doesn't work either.
Piccolo could fire a Makankosappo-esque technique almost instantly upon one year of training, in the fight against Nappa, so it's not a stretch to think he was waiting for it to get properly developed by him until having a shot against Goku. Piccolo also stated that such technique was made so he could kill Goku, so you can't really say it's completely useless.
mg 
