There's two sorts of forcing - there's the lifting the root in the autumn and exposing it to the frost then potting it up and putting it in a cool greenhouse, covering t to exclude all light, so that it produces tender young shoots very early. You shouldn't do this with the same plant two years running.
Then there's the gentler sort of forcing where, in the late winter you put a forcing pot, bucket, old chimney over the plant in situ, excluding any light. This will produce early sweet and tender stalks, but not as early as with the first way. My experience is that as long as the plant is looked after (manured, mulched, watered etc) and well established and as long as you don't overpick and exhaust the plant, no harm is done if you do this every year.