Scott, I've been really trying to think about how I use the fills and how to explain it.
It mostly depends on the song. I use the Break button and the Intro 1 a lot on songs that have real breaks. Examples are Blue Suede Shoes, Tutti-Frutti, Kansas City, Mustand Sally, Boo's Rockin Robin, etc. Sometimes the Rock n Roll style in the 2000 lends itself to certain of these songs and then you can also use the Variation 1 and 2 for some of the breaks. Examples are Your Mamma Don't Dance, Ain't That A Shame, Don't Be Cruel (intro).
On other songs, I almost always autofill to the variations as the song builds to chorus and back. Some fills and variations of course work better on certain songs.
The Yamaha fills are very intuitive and almost always sound as if they fit. It is still a pain to have to manually remember and select which endings to use, but it has now become almost automatic also.
I don't find myself using the fade in and out very much. I can think of a couple of songs only. Fade in on Susie Q, Fade out on Amarillo By Morning. There are surely a couple more, but most of the time I like the song to have a finality to it, especially with dancers.
Lately, mostly out of boredom, I have experimented with some of the Multipad settings to augment or vary the styles. I find myself using Guitar Strum on some of the 4/4 country and blues ballads. For Hank Jr.'s Blues Man, I use the Love Song style, mute the style piano part (bring it in later) and begin with the drums, bass and Guitar Srum multipad on. This changes the style in effect from a piano style to a guitar style.
Just some examples if anyone cares to experiment.
DonM