Well, it might increase pressure but it does as jimjim says.... diverts the pump's oil output to the filter inlet passage. If the plug is out, the oil goes straight into the passenger side oil gallery. It won't loop back through the filter; the pressure where the plug was supposed to be will be a fraction of a psi higher than at the top where the oil filter outlet passage joins so oil won't flow backwards. I'd expect it to slowly purge the air out of the filter and then the filter will be just a static 'wart' on on the oiling system. Any oil drain back protection from the filter will be lost.
