Flash, Splash,Light screen, ANYTHING that does not ATTACK is dibbed useless to me and I never used those type of moves it's a waste of time I like using brute force who else agrees? :D
Fail.
Some of those attacks you say useless are actually pretty good. Light Screen is definitely not useless. It cuts the damage in Special Attacks in half making it annoying for Special Sweepers. Reflect does the same thing except it cuts Physical Attacks in half instead.
Swords Dance is another useful move. When you use it, your Attack power is increased by two stages or by 100% making your attacks do twice the damage. If you can pull off three Swords Dance, your attack power is basically quadrupled. When you give this attack to a Pokemon that already has a good Attack power, their attacks will basically kill any Pokemon in one hit that does not have any kind of resistance to all you Pokemon attacks.
Attacks that reduce your opponents stats are useless though. Stuff like Screech or Charm are easily curable because all your opponent has to do to cure the stat loss is switch out their Pokemon. I rather use attack that reduces stats and does damage at the same time like Psychic.
That's enough of that.
Anyway, besides some of the obvious useless attacks already mentioned in this thread like Splash and a majority of the HM moves, here are some of the worst moves that come to mind.
Focus Energy: In GSC, it was an alright move because it
does increase your critical hit ratio. However, in RBY, the critical hit ratio was calculated much differently. The speed of a Pokemon determines the critical hit ratio which basically makes Focus Energy useless.
Any attack that hits an opponent between 2 to 5 times: Moves like Fury Swipes or Pin Missile are awful because they are weak, inaccurate, and the damage is completely random.
Supersonic: 55% chance of confusing an opponent? No thanks, I'll stick with Confuse Ray if I wanted to inflect confusion.
Dream Eater (Stadium Only): The reason I bring this up is because the Hypnosis and Dream Eater combo is nearly impossible to perform in Pokemon Stadium. Is it just me or do Pokemon wake up a lot faster in Pokemon Stadium whenever you try putting them to sleep? Last time I was playing that game a couple weeks ago, I used Hypnosis with a fast Pokemon to put the opponent to sleep about 10 times. More than half the time, the opponent immediately woke up before I can make my next move. I don't if this was fixed in the sequel because I never played it before.