Adjustable and telescoping ferrules have become very popular in the last couple years. What advantages and disadvantages do they have in comparison to fixed position snap-button ferrules?

Adjustable ferrules give a paddler many more options and make a particular paddle design useable by people with varying paddling preferences. This is a good thing so long as the adjustment system is well designed and easy to use. Telescoping ferrules on the other hand can have strength issues and add additional weight. I feel they should be avoided if possible.