As far as I know, you just get more consistent power and charging. I ran my car (and I drive it, a lot) for 11 years with a generator. It’s not necessary to replace it with the alternator, but I have some power needs (I run 5 gauges and want to wire in a modern internals/stock externals speaker and radio) that I’d like to use in the car. My experience (and my generator was fine), was that at night under the power load of lights and gauges, the lights would dim when I sat at idle, and I would consistently get about 10.5-12 volts on my voltmeter. There is a service that I read about where they can put modern, one wire, alternator components inside your generator housing for a stock look with modern performance, but again, all of this is unncessary if you’re happy with the way your generator performs.