More than you might think... found this today online:
http://www.nytimes.com/2016/03/30/world ... udDev&_r=1
Now imagine a dozen muddy Panzergrenadiers or tank desantniks?
...that tanks either get dusty / muddy / scruffy very easily. It has to go somewhere off the boots.
Personally, many on show at comps ignore this basic issue, beautifully painted or worn, or chipped to excess, but no real filth to be seen.