Reply To: The Bleed and Artwork

Bleed is added to all edges of the page, this allow the printer to trim the finished pages and leave no white paper.
Offset printed jobs are imposed in signature usually 8, 16, 24 or 32 pages for printing, to print on both sides the sheets are often run through the press twice, once for each side of the paper (usually work and turn or work and tumble or printed on a perfecter both sides in one pass) cut into spreads and then bound to make the final book, magazine etc. There can be a misalignment between the front and back print and bleed allows for this.
Offset printed jobs are cut in stacks of 500-1000 sheets on a guillotine so there will be some slight misalignment.

The bleed disappears from view in InDesign when you switch from NORMAL (bleed shows) to PREVIEW (bleed is hidden) the bleed is there it is just hidden from view.

Bleed needs to be added to all pages in your document unless you want a white boarder on your pages.
Bleed on facing pages is a little different in the way it is handled in prepress but just take you art work to the centre fold between two facing pages.