[Hook'em Horns]

1st reason - Bigger, Faster, Stronger!!! Bigger figures can be used at higher weights, The speed of the set can be higher with more weight (at lower weights and higher speeds, figures tend to fall over more), The figs are Stronger with more weight.

2nd reason - Customizing - A lot of time custom poses add on a few grams.

3rd reason - Stabalization of figures - Some figures are top heavy or the design of them are off. The use of weight allows you to balance that figure with th proper placing of the weight

Just my opinion!