They are classed as an insect without wings - they sort of jump. They aren't dangerous but I don't know what they do in the grand scheme of things.

They must do something as they are a very very ancient inhabitant of the world.
They rarely if ever damage plants, either roots or leaves. If found in large numbers it is a sign that the soil is too wet.

They are some of the good guys, they feed on decomposing vegetation and they will do no harm to you.