You can build greater trust with visitors. When affiliate links are used properly, you’ll build even more trust with visitors. This means always directing them to Amazon products that are relevant to the topic at hand. Conversely, any attempts to deceive by pushing them to unrelated links or to untrustworthy products could hurt trust (and get you banned by Amazon), so be careful.
Analytics are limited. Unlike with conversions made directly on your WordPress site, you’ll be limited in terms of what you can learn about the people making purchases through your affiliate links. While Amazon does provide you with details about clicks and sales, you won’t get deep insights into who the consumer was and what they did on your site before they got to that point that you would with Google Analytics.