They can't be used on battery; the discrete GPU will chew through your battery in minutes. They are heavy, loud, hot.
Tried one for a while a long time ago, hated it. I never wanted to bring it anywhere it was so heavy and bulky, so I figured what's the point in having a laptop if I never want to take it with me.
Got a powerful desktop for gaming now, and my portal device is either my iPad or a Macbook air, and I can just remote into my desktop anytime I need.
or not review/understand their required specs,
or both!
So it was used primarily like a desktop, and as my only system having power was useful. But the fact that I could put it in my backpack and transport it was super valuable.
Now I do have a more portable laptop and a full desktop setup. But at the time that wasn't the best option.
I actually ended up buying a travel router and 60% of my gaming was done by remoting into my ROG Ally from my work laptop (they didn't block Steam). The remaining 40% of gaming was done plugged into a TV + controller.
For normal browsing I would use RDP - though it would be amazing if Apple supported some kind of displayport in on the MacBook so it could be used as a screen for an external device.
I've been considering selling my Ally and buying a mini PC with a half decent APU as I seldom use it as a handheld.