Some of the smaller displacement engines with larger turbos such as some of the 6 second cars in NHRA's Pro RWD class (i.e. Titan, Matt Scranton, etc..) These cars have a little 3 liter 2jz with a GT55-91mm turbo. The problem is, with an ordinary two step the cars can only build about 6psi when in actuality they need 30-40psi to leave the line with. This is where anti-lag comes into play. What anti-lag does once you engage it, is that it retards the timing as low as 0* or well into the negative numbers. Of course what this does is causes the cylinders to fire after reaching TDC and the fuel ignites in the header and in the turbine housing. Theres a big difference in sound when these cars are on the anti-lag as there is a massive amount of back firing going on. All this back firing spins the turbine wheel up extremely fast and these particular cars go from say 6psi on the regular 2 step to 30-40psi in about 6 tenths of a second. Anti-lag is only needed when a car has such a large turbo that a 2 step is not enough to get it to the prime boost level for leaving. Anti-lag can also be very hard on turbos as you could imagine with all the back firing and can easily destroy the smaller turbos. The large frame turbos are far more robust and able to take this constant beating.