if your current capacity is limited by the number of frequencies you are allocated, then frequency hopping can help.
Ok, look, perhaps you cannot put more than 3 TRX / sector in your area, because if you do, there will be serious interference. You *can* physically put 4 TRX / sector, but there will be so many call drops, that you don’t gain much capacity by doing so. The extra traffic will be dropped or with quality so poor that the customer will be angry.
The limiting factor here is your number of frequencies. The frequency hopping will allow you to put 4 TRX / sector, while keeping an acceptable quality. The quality is not as good as before, but there is less risk of *critical* interference for one subscriber.