Is it necessary to be crunching data on a machine which has portability as its main selling point?
you can also ask why you should use two computers if one could do it.
hardware is quite cheap nowadays and many things could be done with external devices. For example, if you need a better graphics than your laptop has, just attach it to the egpu. No problem, but then again - why even it is so difficult still today? it should be possible if the manufacturer cant add i/dgpu powerful enough.
you dont need to loose the portability, the main unit (laptop) can be less powerful and do basic stuff but then if manufacturers make it almost impossible to attach e.g. egpu or doesnt allow you to upgrade the device, then you doesnt have any other chooce than have two computers instead of an "upgradable" device.
many have ditched their desktop computers and replaced them by laptops and that is thing to where world is going. for example with egpu you probably dont need to build a powerful desktop machine to be able to attach a good gpu to it.