The I/o shield is mainly there to keep the inside relatively free of dust and stuff. The inside will be dirtier more than normal without the shield. Just make sure to clean it/blow air more frequently. More on reddit.com

I recommend it because the I/O shield usually has tabs of metal that either make contact with the top or the bottom of the I/O connectors while the entire I/O plate itself connects with the entire case. This all act as a grounding plane for static electricity discharge when inserting and removing devices, especially USB drives. Without the I/O plate, you run the risk of blowing the tiny fuses behind every group of USB ports. More on reddit.com

The clip above your Ethernet port belongs on top of the port, behind the plane of the shield. More on reddit.com

Those tabs should be sitting on the inside of the PC on top of their respective ports, not in the ports. You could potentially fry something. I'd pop the motherboard lose if you can or take it out and bend the tabs in proper position, but either way I'd fix it properly. Very last thing to do is cut them off but you still would need to remove the motherboard and i/o anyway and they look like they would fit properly if the bent back in position and the parts are installed properly. More on reddit.com