Sorry, that's kind of a vague question. What I mean is for example, I only listen to LOVEppears when I'm on road trips to certain places, and I only listen to A Song for XX when I'm feeling a certain way. What about you guys? You can list all the albums if you want.
For me:
A Song for XX: I only listen to this when I feel like I don't know what I doing with my life or when I'm just feeling really numb or lonely. Usually when I feel like I've reverted back to a time when I didn't know as much as I do today.
LOVEppears: The first time I ever listened to this was when I was first getting into Ayu and experimenting with her earliest albums. I decided to listen to it all the way through when I was sent on an errand someplace far away that I had never been to before. I got really lost on the way back (MILES away from my house), but LOVEppears kept me company and was very good traveling/lost/exploring music. So now I nearly only listen to it when I'm traveling to some place new or far away. It also brings back a bit of nostalgia from when I was just getting into Japanese music.
Duty: I never really liked Duty when I first listened to it, so I put it away for a long time. Then I pulled it out again about 2 years ago and thought, 'hey, this is freakin' awesome!! Her best from her biggest years are on here!' So now when I feel like listening to old school Ayu at her best I listen to this.
I am...: I used to LOVE this album a long time ago, back when I was into anime and kogals and such; but now it's my least favorite album of hers and only listen to it when I'm feeling nostalgic of my newbie/convention days (which isn't often >_<) or when I'm traveling really really far because it'll bring back that nostalgia and you used to drive to this album.
RAINBOW: I listen to this the most because it's my favorite album, and the first Ayu album I ever bought and the thing that brought me into the Ayu world (it was my experiment to see if I liked Ayu CD). I thought it was unbelievably good (I still do) and the music relates to my personality the most. So not only does it bring back great Ayu nostalgia and is it my favorite album, but it fits my mood almost 75% of the time.
It makes me extremely happy with who I am and lifts up the atmosphere.
Memorial Address: When I'm PISSED. That is all. XD It can fit my raging temperament at the time and calm it down at the same time. And Memorial Address makes me scream and cry in my anger. XD Also, it reminds me of when I listened to it non-stop after I bought it at an anime convention, so I used to listen to it on the way back from every convention (when I still went to them XD).
MY STORY: When I feel like giving this album a chance again. XD Happens once in a while, and then sometimes I remember why I used to like it so much. But then I forget. XD I only listen to this on my computer when I'm doing homework when I know I won't get too into the music to distract me.
(miss) Understood: Good for most occasions for me because I'm bound to have at least one of the songs stuck in my head at all times. XD Also has some of my favorite songs from her, so I listen to this almost as much as RAINBOW. And I listen to this when I'm traveling to certain places that I first listened to it (going to the dentist, going to my friend Emily's house...).
Secret: When I want good hard-core rock songs.
Happens a lot. Never listen to it for the ballads or happy songs.
GUILTY: In the bath. XD And when I'm traveling short distances (I just can't get into the whole 2nd half of the album :/). Also, when I'm feeling really sad I listen to this (the part from Faded-Marionette).