Today I saw someone gaming on a laptop but had attached a keyboard instead of using the built-in. Is this common?
I wouldn't say it's uncommon. Not the easiest to carry around with you unless you have the bag/case for it, but anything beyond a point-n-click game makes sense to use a separate keyboard. Much easier in terms of ergonomics if you can put things (laptop & keyboard/other accessories) in a more comfortable setup. Also protects your laptop from excessively heavy keystrokes impact or shaking the components if you get caught up in the moment.
I wouldn't say it's uncommon. Not the easiest to carry around with you unless you have the bag/case for it, but anything beyond a point-n-click game makes sense to use a separate keyboard. Much easier in terms of ergonomics if you can put things (laptop & keyboard/other accessories) in a more comfortable setup. Also protects your laptop from excessively heavy keystrokes impact or shaking the components if you get caught up in the moment.