It's generally better for employees to have a single machine (that they're very familiar with) to present on rather than having a machine per employee in addition to a machine per meeting room.
But there's the hefty edge case (for developers at least) of showing off a piece of code that essentially requires a developer environment to be running. It's simply not possible to create a developer environment quickly enough in a meeting room for it to be practical.
Meetings are for collaboration, not demos...
Meetings can absolutely be used for demos. Maybe you're demoing for an audience that's large enough to not fit next to your desk. Maybe you're demoing something that you don't want other people to overhear. Maybe multiple people are all demoing projects to each other.