A bad writing group can keep you from expanding your horizons. If you get involved in a writing group that has lost its focus or has become too 'political' to be effective, you may find yourself writng in circles. All of the positive, dynamic members may leave as soon as the group shows signs of disintegration, which can leave the rest of the group in some dire straits. Criticism that was once fair and objective may be left in the hands of someone who has no intention of being fair and objective. The group cohesion, which may have once been strong and vibrant, is no longer present.
Meetings become a chore, and are sparsely attended.
You should be very circumspect when considering any writers' group, even one with a great reputation. It is very possible that the group's reputation is the only thing it has left to offer new members. Never allow yourself to be drawn into a potentially damaging situation simply because the group seeks 'fresh blood'. Look into joining a more dynamic group or consider the possibility of becoming the rainmaker that breaths new life into a dying group. Either way, have a solid goal in mind and work your own plan.