GlennT: I make it a point to play LIVE 'throughout' a song, and this includes during the intros and endings as well. If you don't, it can give the audience the false impression that you're merely playing along with a karaoke or midi backing track, and as an arranger keyboard style musician, this is 'not' the impression I want to give my audiences. I'm not knocking others who utilize midi file backing tracks, but imho the HUGE advantage to 'arranger keyboard' style playing is the LIVE 'spontaneous control' you have that you can't get when playing along with pre sequenced midi tracks. With midi or karoake files, you're merely playing (and/or singing) along with it, while in arranger keyboard mode playing, YOU are the conductor of the orchestra, able to change the song's course at will anytime, throwing in chord substitutions, taking additional choruses, and improvizing when and how the ending will take place.
On most songs, I typically utilize a pre-arranged style ending, but not the style intros. I prefer to play my own intros (utilizing style vari 1) playing variations of standard chord progressions with improvised melodies to lead into the song.
It's well acknowledged in show biz that the first few seconds of a performance (song) make a crucially important initial yet lasting impression to the audience of what you have to offer, so it's important (for me) from the 'get go' to let the audience know that I'm not a karaoke style singer, but both a competent keyboard musician & vocalist, giving them a 100% LIVE show.
There are times when utilizing a pre-arranged style intro may be called for, specifically for tunes which feature a signature recognizable & expected hook intro. In these cases, I always play LIVE, doubling or harmonizing the intro melody line, but playing a different instrument (voice) than the one used in the pre-arranged intro melody. An alternate live playing approach I like to use for endings is to play a counter melody to the line played in the intro/ending.
Scott