I never liked the idea until I started using a browser based pomodoro timer and I enabled the desktop notifications, it's been a useful feature. Now, I'm wondering if there are other benefits I've been missing out on since I have always disabled desktop notifications by default.
Implementing notifications for a timer clock should be included in the wikipedia article about feature creep.
Not minding them too much since I disable them, but at some point it is just not worth it for all the anti-user practices notifications already allowed in my opinion. It just inflates functionality.
In 20 years, if we have even more powerful devices, we will complain about browsers taking ages to load again.