I certainly do not clean every time I fill up an iclear. Whether that be a 30 or a 16. If the juice is getting dark in a tank, it is time for a new head(although you can try a clean and a dry burn.)
I typically clean mine once a week or so when I have time.
Alot of it has to do with the type of juice, and your vaping technique. If you are using a clear liquid, you wont have to clean as often as if you use a darker juice. If you take shorter drags, you will have to clean more often than if you take longer deeper drags. Basically, the coil is burning hotter on longer drags, so less likely for the coils to get gunky, as they clean off the gunk as you vape(at least that has been my experience). Although, eventually, a head just needs to be replaced.