It does not give automatically "better" coverage, but "other" coverage. By the choice of the correct antenna, you can "direct the signal" to where you want to have it. A well sought of WLAN-requirement and solid WLAN design will tell you if you need them or if you can go with the less expensive models with internal antennas. If it is intended for an office environment, you will likely be fine with the internal antenna-devices.
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