I don't keep detailed records, but I do record when things were planted, when flowering started, fruit set, etc. I also like to take notes on varieties, yields and quality. Mostly I like to know I can look back and see how I did things and how they turned out, so I know if I need to change it up or try something new.
I work in agricultural research. At work, I take a lot of plant growth data, such as growth stage, plant height, leaf area, chlorophyll concentration, etc. To make any meaningful assessments based on that data, you have to have detailed climate data to go with it (i.e. daily highs and lows, %RH, PAR, precipitation, etc.) Keeping all of those records can be very tedious.
I guess what I'm trying to say is that my garden is a hobby. I don't like to make more unnecessary work for myself. For me, the end result is most important, so yield and quality is the benchmark I use for my garden. It really doesn't matter to me how tall my tomato plants get, as long as I can keep hauling buckets of high quality fruit out of there. Unless you want to do a detailed, side by side variety comparison, don't over analyze things - you'll just drive yourself nuts. Worse yet, you may end up second guessing your methods - methods that probably work just fine.