Always create a Channels Foundation layout with a white border so that the layout doesn’t bleed. The only exception to this rule is when an ad "floats" among editorial content or other ads, in which case a (0.25 pt) black line should be included at the edge of the ad. The border width should be the same size as the channel on brochures. The outside border width can be equal to the channel width or wider in ads or flyers or especially when final output may be to a desktop printer requiring a wider margin.
Note: Take care that the printer you work with maintains the integrity of equal channel widths. Don't accept a trimmed piece in which the white channel borders appear to be different widths.