This is a simple little utility that sits in the menubar and allows you to control the sleep mode in the Macbook (Pro). You can close the lid and the machine will continue to do important processing, say when you travel with it in your bag etc. I would not expect any problems with heating although of course one uses these kinds of things with own responsibility --- after all, expect there to be plenty of sensors inside your brim that checks the temperature e.g. of the processor. Also, the Macbook (Pro) indeed IS designed to run also with lid closed e.g. with an external monitor and it is just silly that Apple does not buy this piece of software and puts it into Mac OS X Snow Leopard! Anyway, well worth the symbolic fee (shareware). Try it out first, that's the idea of course.