What's the benefits of having a PC for an author

You mean using a PC for word processing?

The mac or PC debate will probably go on forever. The general consensus though is that Mac's are good for graphical work, and PC's are good for business applications and games.

Since your primary work is going to be writing, there is no specific benefit to either machine.

I'd recommend going with what you're more familiar with, and don't let anybody try to sell you more computer than you need.

Just to throw a monkey wrench into your decision, take at look here, and here about Macs running Windows.:)