Chasing Yellow CEL's does anybody worry?

If you don't notice any difference in normal engine performance do you guys worry about intermittent yellow CEL's ?? I've read a few articles that indicated that "euro 348's" don't even monitor/register yellow CEL's. Some say put black tape over them. Educated thoughts??

 

99% of the intermittent ones are just a/f mixtures being off for some reason (o2, temp sensors, maf sensors, etc.) if theres no noticeable performance drop i wouldnt be that scared right off the bat. However, that wouldnt keep me from checking what the codes are as its easy to do. At least id have peace of mind at that point, knowing eventually ill need to get some maf or throttle body cleaner at some point to get rid of it...

 

Mine have been on for at least 100 miles, and while id like them gone, i think i can hold off on replacing my temp sensors a little longer