What is ART?

ART (Android RunTime) can replace the classic Dalvik runtime. The biggest difference is that ART compiles apps on installation, while Dalvik compiles Just-In-Time -> ART uses more storage space, but could be faster to start apps.

Today, ART is not useful for users.

• experimental
• various problems
• creates big cache files
  That's why LX KK resizes /Cache partition to a minimum, and puts the cache on the /Data partition
• if you try it, do it before you install many apps. If /Data is filled up on first boot, KK might no longer boot.
• not faster than the old Dalvik runtime
• today it's only useful for devs to make their apps compatible with ART

...but it's the future.

Android 5 or so will probably make it standard, so everybody must be ready by then.