be good company 是个好伙伴 = to be pleasant and entertaining to be with。
have company 有客人（或朋友）在。
company n.[C]公司。[U]作伴；陪伴；同伴。

【例句】
Am I allowed to have company over?
我可以让朋友来吗？

You'll like Rosie - she's good company.
你会喜欢罗茜的——她是个好伙伴。