An answer or two:
1-The learning feature is supposed to help make the burns better by optimizing things like power calibration, etc., but sometimes a bad burn will affect it. That is when erasing the learned media data is beneficial, because the drive is forced to recalibrate each time (there is no data for it to look back on). There are also times when the initial burns are okay, but it just messes up on the 5th burn (it takes 4 burns I believe to learn the "optimal" calibration techniques with Lite-On drives).
2-See above. Some burns just go bad, and others go okay but with a poor media. Either one of these conditions may throw the drive off, and when it tried to use that learned media data it will (of course) cause issues.
If you don't want to have to "erase" the EEPROM after every 10 burns or so, I suggest you use OmniPatcher to patch the firmware you want. The drive will still learn a small bit of data, but only for one burn, as opposed to 4 or more. This way the drive will be closer to giving you the like new quality (for some this is a bad thing; and for others like yourself it is a good thing).
The main site with the tool is down, so you will find it at the official temporary mirror:
I hope I managed to help you.