i only cut the spikes if the tip dies out. most of the time if it stays green, it will eventually grow some more buds. if the tip does die, then i cut it back just below the first old flower notch. the little bracts that show like a join on the stem can produce a new branch sometimes. some people just cut the old spike off, assuming that the plant will grow a new stronger spike because it is not wasting energy to produce new buds on the old spike. i have had some put out new spikes while the old one was still going though, so i'm not sure how critical that is.