Sensor is just their for you to get grand items- and EXP when you're bored. But if you look at the right person, like western paladin said- you can get some specky items.

I don't use it because I know my way around getting the good items you can by using sensor.

You can get:
Materia blade= Ultima Charge/Sword (Mogknights/Gladiators) - Treasure Hunt
Zeus Mace= Ultima Blow (sage)- Treasure Hunt
Zanmato= Ultima Masher (Viera)- Skill Level up... I think
SeventhHeaven= Ultima Shot (hunter)- Shara- steal it or get her in your team, Or buy it off the shop waaaaaaaay later in the game for 20000 gil (but don't worry about the price- by then, you'd have heaps of gil).