Is it harmful to macbook to display on monitor at all times?

Just wondering if it is harmful in any way to have a macbook hooked up to a monitor 100% of the time. I noticed since I leave the lid closed when I do this, that the macbook gets incredibly hot due to it running with the lid closed. I would leave the lid open but i have little space and it is easier for me to keep it closed. Will this harm the internals or something? It seems like when I close the lid and then wake it up with my mouse, I am almost tricking it prepared to be in sleep mode, and making it run hot.

Any opinions? Thanks