The torque converter mods are typically used to help stall speed.

Ex. you have a high HP engine and want to build rpm higher to launch or don't want to hold your brakes down as hard at the traffic light b/c your car actually pulls that hard w/out any gas pedal pressure.

In these cases raising the converter stall speed lowers its tempreture and helps your high hp car run better. You may just want your car to rev a bit higher before the tranny hooks up. In this cases a modified converter is nice. If your car is stock you may not want a converter.