Spy is a great addon. There is a reason it’s so immensely popular, people love it. It really makes world PvP a much easier and more enjoyable experience.
Rogue tries to sneak up on you? Nope. Spy notification, pop perception, death coil. Threat eliminated. Rogues were too overpowered anyway, Spy balances things out. Blizzard should make Spy a standard UI element just like how they have done with other popular addons. It would greatly benefit the world PvP scene since rogues are too overpowered without it.