Yes! Think of it like the difference between a portable Bluetooth speaker and the speakers in your living room. The latter may sound better and go louder, but you can't exactly pop them in a bag and take them to the beach. Even taking them into the garden is an enormous pain.
It's the same with portable projectors. They're typically – but not always – less bright and less powerful than their wired siblings, but they compensate for that by being incredibly practical with go-anywhere abilities. Battery-powered portable projectors are more than capable of delivering movie night without you having to worry about finding a power socket, and their portability means they're easy to move around and very simple and quick to set up.
That doesn't mean they're just for the great outdoors, though. Because portable projectors are designed to be small, they're useful for rooms where you don't want or can't have a normal-sized projector, or for homes where you might not want the projector in the same room all of the time.
The main compromise with portable projectors is in brightness: that's the biggest drain on their power, so battery-powered projectors have to strike a balance between the brightness of the picture (which in turn affects the maximum range and size of their display) and the amount of time they can run for between recharges.