depends on how well tuned the motor is to begin with, and the other changes you've made to the motor that will affect a car.
for instance.
stock 5.0 mustang , chip might give you 1-2hp of 225hp at peak 5500rpm.
turbo eclipse, chip will allow raising of boost 2x stock, giving 100-200hp. (if you're motor doesn't barf).
older BMW's (my 750il) gets 45 peak hp, and 30peak ft/lbs of torque. It drinks 14 miles per gallon from the 5.0 V12, so how can i afford to put 92 octane in stead of the normal 87.
If you've got a worked motor, with better breathing, or a power-adder, then new fuels curves (superchip) are a must. gains of 50hp with a 9lb blower, ported polished intake, k&n, worked heads, and new exhaust , are not uncommon.
a honda civic, hehe, might get 1-5 hp, which is nothing.
since any car with less than say 200 hp, and 200 ft/lb of torque is a wussy car to begin with.
Added power = added stress, and less duration of motor parts. Also some chips will (regardless of what they say) fail your emissions. If you bring your car in for warranty work, you BEST remove the chip first.
The chip should be last among the things to spend money on when making your car faster. they don't do much at all. A cold air intake, underdrive pullies, short throw shifter, maybe even a new exhaust cat-back are MUCH BETTER examples of how to get more performance out of your car , for the same money.
Seriously, don't buy a chip and a TYPE-R sticker, you'll asking to get spanked by somebody. Work your way up with some real mods, and learn to drive your car faster.