So I'm having to start over in retrogaming, and have been looking at AES systems on eBay (as well as MVS, but this concern is just with AES). Quite surprised how many are pointlessly sliced up to install component jacks/composite jacks/etc. What is wrong with the RGB from the stock DIN? And if you need component, use HDRV or a Retrotink RGB2COMP. It kind of depresses me.
I used to mod AES systems and sell them on eBay about 15-20 years ago. There are a few reasons for this. First, US TVs typically did not accept RGB at the time, and finding something like an RGB2 was very difficult and most people in the market for an AES didn't even know it existed.
Second, the AES A/V cable only has mono audio, so having stereo RCA jacks was a great way to hook it up to an audio system. Sure you could use the headphone jack but then you're going through a couple adaptors and it's a pain. Again - the regular Joe wouldn't know how to do that.
Third, I would put a light in the reset button as a power indicator, something that was missing from the AES and seemed like an oversight.
Fourth, depending on the serial number, most systems benefitted greatly from an RGB bypass mod to bypass the CXA amp and take the RGB signal straight off the DAC. While that enhanced the video quality significantly, it also disabled the composite video out on the stock DIN, hence the need to replace this with a video encoder board and alternate video outs on the back of the shell. Again, US TVs at the time couldn't do anything with the RGB so this was the only way to do it if you wanted a good picture.