这里的bring是及物动词,可以带双宾语或宾语+补语。该句属后一种情况。 with it就是补语,其中it代表天气(比如,it is sunny.)。如果把语序换一下,就好理解了。
……had brought clouds so sombre with it.
它在哪方面的用途决定它的社会价值。
还原:The use / to which it is put / decides its valuce of society.
= It is put to use,and the use decides its value of society.