I personally do not like having any cases on laptops, but some people in our organization uses them. When I have to remove these covers to repair the laptops, I find dirt & crumbs behind the case, many times grinding this dirt into the aluminum. It is really disgusting. Sometimes I can clean it off with some cleaners, but other times marks & debris remain which I cannot clean or remove.
Most of these plastic cases are cracked when I receive them. Sometimes I have almost dropped the laptop because the laptop actually slips from the plastic case.
Plus if the laptop needs repaired, the case will need to be removed. Removing the plastic case from the Display is very tricky...I hate doing it since I feel like I'm going to crack the glass or the LCD Panel since the displays of current laptops are so thin.
You would be better off placing the laptop into a nice travel case laptop bag, just don't put anything else into the bad or you risk damaging the laptop.
Just my two cents for what is worth.