I have a 1×1 11b/g/n Wireless LAN PCI Express Half Mini Card Adapter in my laptop. Will it be of any use if I buy a USB WiFi adapter?
Purchasing a WiFi adapter will be of no use to you unless your internal adapter for some reason breaks. Your internal adapter will be quicker and more reliable, and since you said it already supports the 802.11n standard, you already have the latest and greatest - no need to buy an adapter for that reason, either.
1)internal wireless cards will always take precedence over external wireless if no
settings are changed or the internal card is not disabled. use the hardware profiles to disable the internal WiFi when I want to use the
2)USB is slower than internal cards.If your internal card is wireless b/g and you acquire an external wireless N
card, the external N card will be faster than the internal b/g card.
If the internal card is capable of N performance it will outperform the USB
Adding External or Internal WireLess LAN Antennas for Laptops & Notebooks
It depends on your use of the wifi adapter......its useful if you are using it to connect to some wifi network which the adapter of your computer does not detect because its out of range......some usb wifi adapters are much powerful than inbuilt adapters.
Its true that inbuilt provides much more functionality but usb adapter provides better connectivity.....
To tell you the truth.....its not really required for basic users...
It really depends on which USB adapter you want to purchase, as we need to compare the specs. However, in general - the internal wireless adapter will offer more functionality than an independent USB adapter.