Why so many current BE automatic(?) snapshots?

I was checking BEs after updating from SRU 14.5 to 15.4.The SRU versions are probably irrelevant to my question: Why so many current BE automatic(?) snapshots?

# beadm list -a
BE/Dataset/Snapshot                             Active Mountpoint Space   Policy Created         
-------------------                             ------ ---------- -----   ------ -------         
11.1.14.5
   rpool/ROOT/11.1.14.5                         -      -          18.48M  static 2014-01-03 14:41
   rpool/ROOT/11.1.14.5/var                     -      -          8.81M   static 2014-01-03 14:41
11.1.14.5-backup
   rpool/ROOT/11.1.14.5-backup                  -      -          58.0K   static 2014-01-03 14:44
   rpool/ROOT/11.1.14.5-backup/var              -      -          1.0K    static 2014-01-03 14:44
11.1.15.4
   rpool/ROOT/11.1.15.4                         NR     /          11.41G  static 2014-01-23 07:13
   rpool/ROOT/11.1.15.4/var                     -      /var       1.73G   static 2014-01-23 07:13
   rpool/ROOT/11.1.15.4/var@2014-01-03-16:44:42 -      -          167.48M static 2014-01-03 14:44