As is often the case的意思是“像往常一样”.如果这个短语你觉得不好理解,你可以更换一下次序,把"the"提前--As is the often case,就像往常那个案例/那种情况--这样是不是舒服点了?而英语里而定语（often）前置的倒装句是很常见的,所以~
举个例子：As is often the case,I gave up dieting and started blaming myself at the 2rd day.像往常一样,我在计划减肥的第二天就又放弃了,并且开始自怜自艾.---本人自造的句子,完全表述了郁闷的自身情况,哈哈.
ps,关于你问的as的全方位用法,我不太理解,是要as的所有常见用法么?请看这里