Here is a little piece of free software that you don't realize you need for your Mac, particularly your MacBook laptop. Caffeine is a free utility from Lighthead Software that just sits in your menu bar does one thing very well. If you click it's coffee cup it fills with coffee and your Mac will not go to sleep, the screen saver will not engage and the screen will not even dim to preserve power.
Sure you could click a bunch of things to do this, but Caffeine makes it painfully easy to engage at will. Why do you want this? Anytime you want to watch a video clip, or read a long blog post, I find it great to click and not worry about my screen dimming away on me. Working on a complicated problem that you need to just stare at and analyze? Click the coffee cup.
I use this way more than I ever would have expected.