It is ok to use your laptop with LCD lid closed. Ensure that you always use it on a flat surface. It also depends on how much heat goes through the keyboard as LCD screens may heat up due to this. This may not be good for the LCD on a longer run.
Thanks for the answer. My concern was mostly regarding ventilation holes that are just above keyboard (unlike for instance in inspiron series, where the holes are by sides). I'm not sure if the holes are for breathe in or out. And I will keep LCD off when the lid will be closed.
Could you please comment on this?