Niko Neugebauer talks about handling sequences and default values within columnstore indexes:
There are still no dictionaries – and trying to rebuild this table will not bring any effect at all, but take a look at the size of the segments – their size was lowered for almost 40% to ~1.6 MB!
This technic is very effective if you are compressing the columns that you do access rarely – it should be considered for the log tables for example.
Also notice that Columnstore Archival compression will not bring any significant changes – the original 2.6 MB will lower to 2.42 while the variable char column will not get any further improvements, making the improvement difference around 32%.
Warning: Do NOT use this technic without understanding the consequences – the processing of such columns will lower their effectiveness, since Predicate Pushdown will work in a very limited way, plus the Segment Elimination will not work at all.