Do you mean the night time shows on the Theater and ToT, or Fantasmic?
For Fantasmic, you can do a meal plackage or FP to get a reserved seat. They tend to be better than the standby seating, but non ie bad. Even with a package or FP, you will need to be in line 30-45 minutes early.
For the fireworks shows in the Theater, there are dessert parties to get reserved seating. We have just done unreserved seating, (find your own space) and always been able to find a good place to view. If you will be there during an extremely busy time, the reserved seating may be the better option.