Easy to create segments, easy to add tags that are relevant to each campaign (like website).
The UI could be more intuitive - it would need some improvement in order for me as an advertiser not familiar with all of its features or how they work together. My email client was unable to see any information about my campaigns when I used this tool alongside Mailchimp. It really is amazing at helping you get started quickly without having too many bells & whistles but also allowing lots of customisation options if needed later down the line!