You have to ask yourself questions (and give more information).
1. Do you live out in the boondocks, or in the city?
2. Who/(what) are you trying to listen to? And, conventional or trunking? What band (vhf/800/?)
If you can already get what you want on your desktop, an external antenna is overkill.
But, if you live out in the sticks... then, yes, you will benefit.