It's a pity Raticate is so fragile, since it can work if you are careful, and it is pretty cool. Super Fang really is a great move.
There is only one reason to use Raticate: Super Fang. Super Fang + Hyper Beam is a 2HKO on Starmie with average damage, so anything weaker is pretty much reliably KOed, while everything else needs a little extra help. But seriously, if you think about it, nothing other than Golem or Rhydon can manage that feat, and they are beaten by BubbleBeam. Nothing resists Super Fang, so you don't have to worry about being outpredicted.
Send Raticate out when you would send out any other physical attacker, and Body Slam or Super Fang, depending if you have paralyzed their fast Pokémon with recovery moves or not. With a little luck, you can dismantle your opponent's whole team with a Raticate, of all things.
Focus Energy is an option if you are playing on the old bots or on Stadium.
Checks and Counters
Raticate is a very unique Pokemon since he automatically takes off 50% no matter what; in other words, tread carefully when trying to counter him. If you paralyze or sleep it, you essentially render it useless.
Gengar is a top-notch Raticate counter, but even he loses half his health on the switch since Super Fang affects Ghosts in RBY. Basically, the best option is just to hit it really hard with the Pokemon you currently have in. Excellent counters are Pokemon such as Starmie that get Recover; use it immediately after Raticate uses Super Fang or you'll be OHKOed by Hyper Beam.
In UU, Porygon has Thunder Wave and Recover, but must beware a Hyper Beam after a Super Fang, since it will KO Porygon without a doubt. Tangela isn't KOed and packs Stun Spore as well as possible recovery in the form of Mega Drain with Growth.