Glock plugs are really a matter of personal preference. Some argue against them for reasons of debris retention. Others, including Larry Vickers, argue for them postulating the plug keeps debris out of the pistol.
Some argue against them for magazine rips in the event of a failure to drop free. Others say that's not an issue in the real world.
I believe the open channel exists to simplify the manufacturing process as well as facilitating a snap-in shoulder stock to enhance the efficacy of the full auto version Glocks.
Plug it or don't plug it. Just shoot the sh!t out of it at every opportunity