The plasma intercooler was a starship system used to provide plasma coolant to the warp drive and other critical systems.
A failure of a plasma intercooler will cause the warp drive to overheat or possibly fail to work altogether. (TNG: "Relics")
Chief Miles O'Brien took the safeties of the USS Defiant's plasma intercooler offline and never had any problems. Ensign Nog did the same on the USS Valiant in 2374. (DS9: "Valiant")