You will hear sound arguments for and against the case. It all boils down to what you would prefer based on your specific needs. As for me as I was struggling to decide between case vs. skin. vs. sleeve, I opted for a sleeve. Why?
I'm always very careful with my gadgets when in use. Though accidents do happen, it is so rare for me that I figured having a well constructed sleeve would be best. I would not have to worry about regular dust removal, as the case would be had I purchased a hard case. Nor worry that the hard surface would scratch against my macbook due to friction while in my bag (I'm a student with many books to carry). The most I might do at this point is purchased a palm guard and maybe a keyboard protector, but I'm still debating whether those purchases are necessary.
Do what pleases you aesthetically, cost wise and in function. The options are endless and if you're super OCD and have the cash to support it, run crazy and by the skin, hard case AND sleeve.