[Nanolathe]

As long as you can get the Pulse rifles hitting you'll find Orks, Guard, 'Nid and to some extent other armies like Eldar/DE (Guardians/Warriors) will get their armour saves negated. Elite squads like Nobs and Kasrkin, Genestealers and Aspect Warriors will still feel the pain, but get a pesky save. Try to light up (Mark) elite enemy units for maximum pulse rifle damage or Carbine suppression. Then again you must remember that Fire Warriors are not the only unit in your army. Try using something like XV8s to mow down anything with a 4+/3+ armour save. A tau army is all about specialisation, the right unit for the right job, much like Eldar. Don't waste a precious shooting turn with ineffectual targeting. Your Shas'La will want to be shooting at the rank-and-file infantry first (or something that is trying to assault them) to make maximum use of their weapons. That said if you really have nothing else to shoot, Tau Fire Warriors are the only basic infantry with a weapon strong enough to take down a Wraithlord ( T8 )...

"Shoot what you will kill fastest, or what is trying to carve you a new belly-button" is my Motto with Tau.