Black & White
Black & white works well with pictures of people & sometimes landscape alot of the time you need the colour to tell you about the image if you dont have this the image can be a bit plain! you want the people looking at it to be intrested and all of a sudden look at it.

Colour
Of forest, water & animals colour is a good thing to have it brings life to the image!
Of a forest the beautiful greens come out in the image & of water the colour of the blues & the effect of the water is effected by your camera.

I'm not that good with photography to add agree or disagree with the above statement

I turn my photos black and white when i was to create a certain dark/uncomfortable mood or when i'm want to make a portrait stand out by varing the coversion process.

As far as color i try to saturate the photo to make it more vivid and make minor adjustments with the curves tool to make blacks blacker and whites whiter. If it is a landscape portrait I wouldn't want it to overcome my subject so I might tone down the color a bit.

Black and white photos can appear to be sharper and will increase clarity if the picture was good to begin with. It can also attract attention (grabs the viewer's eye) when used appropriate in places with lots of colours around. Of course, all of this is assuming you mean grayscale; black and white would strictly be #000 and #fff.

Colour adds life and brightness to the image, but can be dulled out if it is too saturated. Depending on the nature of the image, you may or may not wish to use colour. Blues, purples and greens are considered to be cool colours; reds, oranges and yellows are considered to be warm colours.

For me, it depends on the photo I am taking. If it is of a wonderfully vibrant colourful scene I will take it on colour. Otherwise, I'm a real fan of B/W (or grayscale ) photos (also, sepia tone is nice!).

B/W photos only really work in a bright environment, i.e. outside in the sun and I don't think work as well indoors with a flash. One of the major upsides of developing my own photos is that I can perfect the tone of the photo to whatever suits!

On my (Cybershot) phone, Saturation is a really good effect. I don't think I have Greyscale, but nearly everything I've taken pictures of, also with proper cameras, have been sunny stuff.

I too am a huge fan of black and white photography. Sometimes color is almost a necessity (a beautiful garden full of vibrant flowers, for example) but many times black and white adds a clarity and sense of respect to a photograph that I find very appealing. I'm sure a large portion of it is personal preference but at the same time certain technical aspects of either might be pretty much set in stone.