So... your average rock band. When a lot of people think of this most epic of set ups, (Note: This Is Not Everybodies View I Know, I Am Just Using This As An Example) they think of electric guitars, amazing singers, a wild (although not always) drumkit, and perhaps the all-important bass. However, many people tend to overlook the humble keyboard.
I happen to be the keyboard player in a rock band, and whenever anybody asks me "what do you play?" and I reply, "the keyboard" they just sort of say, "Oh." and walk away. If any of you have had a similar experience, please don't hesitate to post a comment about it.
Keyboards, by some peoples standards, are not "cool" enough to be in your average rock band. For one thing, the player is somewhat limited in their movements and may not have as much stage presence as people playing other instruments, however what they lack in looks, they make up for in depth and quality (By that I mean what the keyboard lacks in looks, have you seen David Bryan, the Bon Jovi keyboard player's hair!?)
In many live performances, keyboards can be the essence of a song. It is a fact that when many songs are being recorded, the guitarists usually have to add in a few extra sections on top of the main rhythm to give the song more depth. For this reason, they have no need for a keyboard player when recording, however on stage this sort of backfires.
On stage, you cannot go back and add in more guitar parts to give a song more depth, and this is where the keyboard comes in handy.
Be it a flowing, electric synth, or a binding and elegant piano solo, the keyboard is just about king of holding songs together and giving it character. Because don't all successful bands start off with amazing on-stage performances? Some people may argue that they don't want a synth or keyboard in their songs, because it doesn't fit in with the song that they are doing, and my argument would be that hey, keyboards do have guitar sounds too!
Now I do not wish in anyway to undermine heavy metal bands, and that is perhaps the only time I can think of where a keyboard is not necessary for on stage character and depth, for most of this is achieved by extremely loud playing by multiple guitars, as well as vocally challenging on stage singing.
I am aware that you may also argue that keyboards are used in POP music on stage to create amazing electric synths, and if there is anybody out there who hates the genre then I'm sure that they would be less inclined to include a keyboard in their band. However I am sure that many of the people who will look at this have no interest in the likes of Justing Beiber, for there is clearly no need for a shining guitar in many of his "performances."
In conclusion, I beleive that the keyboard is a vital addition to any budding rock band, and I hope that you will all agree with me.