Table width is quoted in percent (width divided by the average stone diameter). Table size is less critical to the beauty of a diamond than variations in than crown and especially pavilion angle.
Larger table diamonds and can be brighter, (i.e. they return more light), but are often less "firey" than diamonds with smaller tables. In smaller diamonds below 10ct, having a larger table size can be advantageous.
The ability of a diamond to break light into rainbow colors, called dispersion, is enhanced by light entering or leaving a diamond at an acute angle. A larger table size means a smaller crown facet area, (the part that creates most dispersion). The same principle applies to cut crystal wine glasses and chandeliers. If you look from the front of a diamond you are more likely to observe dispersion from a crown facet which is greater in size when the table is smaller.