with意思倾向于并列.例如是朋友间（同级的）的陪同.
而by的意思倾向于被动.
例如children under 14 must be accompanied by adult.长辈对晚辈的陪同.
The candidate was accompanied by six burly bodyguards.对主人的陪同.
your application form should be accompanied by you CV.申请表格应该附带简历.
be -nied with (a thing)
带着,带有,兼有
(be)-nied by
附有,伴随
但如果真的用起来,其实没有很大区别.