Assuming you have a spare slot (and your laptop is designed in a way to make that swap easy)

Some laptops have gone the Apple route and soldered down their storage. Other laptops have a whitelist for hardware they’ll accept (though that’s mostly for WiFi cards). There are some real shitty laptops out there.

With modern USB speeds, that still shouldn’t be a problem, but there are situations where upgrading the SSD isn’t an option.