Armchair Traveler

Hi-I apologize if this subject already has a topic thread. The Cruise Critic search engine does not seem to work (at least when I have tried). We are on the Ruby Princess Coastal 10/26 sailing. I have a couple of cruises I am looking into. What are the pros and cons of booking my next cruise while on my current one? Travel agents have perks (and Costco has the Costco Shop Card gift)! Any thoughts are appreciated.