A few years ago, I put aside all friendly warnings and dismissed my trepidation and started mixing my own glazes. I promised that I would report back on how it was going and I'm happy to say that I'm more than delighted with the results of my experimentation and have caught the bug for testing new glazes. At this point, I've eschewed all "commercial" glazes (not that there's anything wrong with them) for my own mixes; I can get a ton of unique variations with the layering, get more specific with the colors in my favorite tones, and I'm saving money as well. While commercial glazes are generally very reliable, they are also mostly selling you water.
Once I started collecting a few recipes from sources like Glazy , ICAN, and Digitalfire, I began to understand what kinds of glazes I liked best which turn out to be lots of greens and blues which happen to be the easiest and most forgiving to work with. I settled on a few favorites and began testing other colors. The hardest ones to get have been the purples and reds and have taken the longest to achieve in reliability and durability.
Glazes that don't work out -- perhaps they craze or pinhole on my clay bodies, or I just don't get the color I thought I would-- don't get thrown away but mixed with another glaze that might also not be working. A glaze that crawls and is too "stiff" might get mixed with another one that's too runny. I've had some success with this and it keeps waste to a minimum. Others might be fine except for the color, so I might just add a stain to improve it and -voila!-- I've got another unique glaze.
It's been quite fun experimenting and I'd recommend the journey to any serious ceramist who wants to deepen their practice.