1. SDC is huge for me, it's allowed me to get home earlier from a trip on business travel and has also allowed me to extend vacation on personal travel (especially around holidays when I've booked a cheap fare for say Sunday of Memorial Day weekend and then been able to SDC it to Monday evening)...I fly DL enough to be silver and their 3 hour limitation is a killer
2. From DCA / IAD it's more convenient for non-stops especially transcon (AA DCA - LAX v.v is at terrible times)
3. Customer Facing Technology Interface: This might be a little more disputed but in my experience once I knew all the tricks and tips to navigate .bomb/mobile.bomb/.bombMobileApp, they actually provide much more information (fare classes, plane tracking, etc.) vs. the other majors, which can make a huge difference as often this information comes in handy during IRROPS when dealing with the 1K line (the flip side being the 1K line should have this knowledge without me force feeding it to them but that's another thread)