What value can I gain by doing exploratory data analysis on features (and thus data) before doing clustering?
How would you know you have to do cluster analysis before looking at your data ?

Setting aside data quality questions (which you should never do), a bare minimum of EDA will help you :


Know if it's relevant to do a clustering analysis (rarely imo)
Know if K-means is the best clustering tool (rarely imo)
Get an idea of the number of the clusters


Then you should do some EDA after, to understand what are the clusters you have selected. 

Edit: Basically, it will help you answers this kind of question : How do I interpret my result of clustering?