CapTable contains process variations such as wire width, spacing and temperature coefficient of resistance. It contains capacitance information w.r.t wire width and spacing for all metal layer. Captables are used for calculating RC delay.
There are lot of RC corners in which you can time your design. You need a capTable for each corner in which you wants to time your design. Dominating corners in most of the designs are cworst for setup and cbest for hold.