I like that it can be used to create new posts or pages from an RSS feed, as well has importing existing blog entries into wordpress so you don't have duplicate articles in your site! It's not perfect but there are some things we haven’t been able yet solve with this tool - such us custom fields (for example product categories) which would make our life easier if they could do them somehow :) We use wp-site importer almost every day now when creating news items about clients/products etc., instead of copying& pasting those data manually via copy & paste option provided by Word Press itself ;) This way all information gets imported automatically without any manual work needed afterwards :).
And also very helpful after publishing something because sometimes people forget what was published before where exactly ;)). Maybe adding more options will help solving problems users might face while.