Supposedly it slows data transfer down with normal AirPort. Someone tested this, and didn't really find this to be the case. I haven't found it either. There should be no real problem - I haven't noticed anything and use AirPort a lot.
Incidentally - I understand the conceptual argument for not enabling wlt1 (i.e. that your system kext list remains pure as the day it shipped from Apple), but is there a practical reason not to do so?