Logistically physical meetings have several disadvantages.
- Must somehow cover travel costs of participants. Often this comes out of the conference budget, raising registration rates.
- Since traveling overseas is difficult just for a committee meeting, physical PCs have less international participation.
- Invariably some PC member misses the meeting and has substantially less influence on the choices.
The dynamics of physical and electronic meetings differ. Both start by quickly accepting the strongest papers and rejecting the weakest. In a physical meeting the remaining papers get discussed serially. There is a tendency to accept more often at the beginning, realizing you accept too much and start being more stringent and bouncing back the other way towards the end. One also spends too much time talking about the first set of papers, leading to rushed discussions later on.
In an electronic meeting the discussion on all papers happens in parallel. When discussion seems to go a certain way, the PC chair will suggest acceptance and rejection and sees if someone objects. A vote is taken for a few contentious papers. But many papers have nobody who loves or hates them. For those the PC chair has tremendous power for no one will object to whatever they recommend.
Both types of PCs suffer from groupthink, a tendency for groups to reinforce viewpoints. A PC chair also has to make sure that everyone participates in the discussions.
My preference goes for a third approach that I have seen used in a few conferences. The PC members send their reviews to the PC chair who, after some emails for clarifications, makes all the final decisions by him or herself. Simple and, with a good PC chair, works surprisingly well.