If groups meet in person, members can read each others' work aloud. That's helpful because intonation patterns or stumbling over awkward phrasing can reveal a lot. Internet critique groups can include members who live far apart, use different dialects and have different experiences so they offer different perspectives.
The first kind of group may meet in homes or public places, and the convenience of the location must be taken into account. Obviously internet access is necessary for online critique groups and all members must be able to open each others' documents unless material is copied and pasted into e-mail messages.
Physical meetings need to be held at convenient times for all members, and frequency must be considered. Many such groups have monthly meetings and some writers' deadlines might come between meetings. Internet groups need to be well moderated so all members can post equal amounts of work and do their share of critiquing. It helps if a schedule for posting material is agreed on. Frequency is also a factor here.