The ability to have an auto responder that sends out emails at specific times depending upon which day of week they are in can be helpful when you don't want customers getting email after being off their website or not responding right away! This is more difficult than it should really be as far as implementation goes - there seems like this ought to be fairly easy but I haven't been able to figure how/where to do it properly yet without using multiple plugins with confusing names and settings options etc.
It's also annoying having people get so many emails from us because we're sending them information about discounts/sale items and then forgetting why they were signed up or who they belong too (I'm sure some other businesses face these issues). As mentioned above though if someone isn't engaged enough to log into our site they won't engage further anyway so perhaps its less important?