It’s a complete pain if you use a laptop as your daily driver. You don’t want the entire drive filled with photos, and using an external drive with Apple Photos is a PITA as the integration with iCloud doesn’t play nice if the drive isn’t reliably attached.
Apple would make a lot of lives easier if they made a tidy way of exporting images from Photos easier to automate. And while they are there, a photo file structure that wasn’t horrible, with photos names something like ‘date-time’.