This is used when you are adding that something may be even more, less, better, worse etc than you have just said. 即使不是更…，虽然没有过多…

• Most of these gizmos are as insecure as any other computer, if not more so.
  这些设备像普通的电脑一样不够安全(很容易遭到攻击)。(这些设备中的大部分即使没有更易遭受攻击，也和其他电脑一样不够安全)
• Her needs are just as important as yours, if not more so.
  纵然她的需求不更重要，但至少和你的一样重要。

You can also say if not impossible/great/forgivable.

• The snow was now two feet deep, making it difficult, if not impossible, to get the car out. (if not impossible = although it was not impossible)
  雪有两英尺厚，要把汽车拉出来很困难，尽管不是不可能。
• Although governments and large companies are crucial in addressing conservation issues, the role played by individuals is just as important, if not more so.