WHS keeps backups on the schedule that you set. By default, I believe it keeps backups for about three months, but I don't remember the exact number. I set WHS to keep backups for six months and set a couple of older ones to be kept forever. Generally, it takes very little extra space to keep extra backups because only one image is kept of unchanging clusters on the hard drive. Also, any manual backups that you make are, by default, kept forever.