With basic economy you lose ALL flexibility (the entire ticket is use-it-or-lose-it for the exact flight you booked) and any elite seating advantages (you can only select a seat at the back of the plane and you can't get upgraded to premium or F).
You don't anything else. Miles earned, boarding group, and checked bags remain the same.
IMO the seating restrictions aren't that big of a deal on short flights but the flexibility really is. SDCs aren't worth much on a long flight that only operates 1-2x a day, but they are extremely valuable on a shuttle route that operates 7x per day. If you are flexible, you can often save a lot of money by buying the cheapest ticket of a particular day and SDCing to one at a more convenient time. Also, it can be really useful if you just don't know when you will be ready to leave (eg, if you, are flying in for work, which may run late)