Here's another example of how watchOS 2 will, potentially, improve the experience of using apps on Apple Watch. August announced an Apple Watch version of their app to unlock smart locks with a tap. Because of WatchKit 1.0, it wouldn't be uncommon for the August app to take several seconds to launch, be slow, or occasionally crash. Exactly not the kind of experience you'd want when standing in front of a locked door that you want to open with the convenience of a smart device (just use your keys at that point).
The couple of watchOS 2 apps I'm using so far are already considerably faster and more reliable than their WatchKit 1.0 counterparts. While not completely native to the Watch, watchOS 2 apps will benefit from speed improvements besides access to sensors, and that should help companies such as August when it comes to everyday performance and enjoyment.