If you use a clean, good quality, fuel you don't need additives. It isn't like preventative medication, it is putting something through the combustion system that wasn't designed to be there. If you have build-up of contaminants in your fuel system, a treatment of Tecron may help, but you would be better off to use better quality fuel to start with, as the treatment process can loosen particles that can then clog injectors, etc.

__________________
2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue