DIY CO2...why anything else?

I have a very basic question I would like some opinions on.  I have been
using a DIY CO2 injector with yeast for years now with great success.  I
realize you can not control the CO2 output as well as with comercial versions
but I have never had any problems.  Once you come up with a recipe that works
well with your tank...the result is the same IMO.    I have followed the
postings on the topic of CO2 for quite some time but would really like to
hear how all of you feel about this.  Why the expense of it is not necessary?