Image by rpavich.
Here the egg adds a fluffy, almost buttery texture but retains a neutral flavour to soak up the flavours of anything else you add.
When I first told our own Alan Henry about adding an egg to porridge, he was not totally convinced this would create something edible. He's wrong, clearly. The key here is to first cook your oats midway (in the microwave or on the stove). Crack an egg into another bowl, beat it, and whisk that into your still-cooking oats (or pause the microwave and mix in the egg before shoving the oats back in to nuke for another minute or so.)
While the egg cooks, it puffs up and adds a bit more volume and texture to your oats. Add more liquid if you want, until you get your desired consistency, but it should come out thick and creamy. Plus: hey, some protein!
Why You Should Cook an Egg into Your Oatmeal [Huffington Post]