Over time VG leaves a clear slightly greasy film on surfaces. The higher the percentage of VG in a juice the faster this film builds up. PG also leaves a film but not to the extent VG does. This film builds up faster when Sub-ohm vaping since you consume more juice in a shorter period of time, the more juice you vape in a day the faster this film builds up. Even so, vape residue is easy to clean off, much easier than the tenaciously sticky yellow/brown tar deposited when smoking cigarettes/tobacco. That stuff was a nightmare to clean.