Unless the rule has changed in the past month, the extra "Y" segments book into L on AA and into Y on AE and AC flights -- a great benefit on the CRJs as this makes for easy availability, but not a more comfortable seat or flight. The L can be upgraded per normal Aadvantage rules (including the 100 hour EXP free upgrade) but doesn't book automatically into First. AA seems to let you pick which sectors to buy, while BA insists it is always the last ones that are "extra". Nothing in the rules actually clarifies this from what I can tell and the results are random. Buying extra segments is still worthwhile in some cases as you get a fully changable and even refundable ticket for the extra segments (only), but obviously this eats into the 20 sector limit.