I used to cut mine only when they got to be over 3". And those "spikey" things may develop into a split in the rhizome (like a Y) But I would let it go for a while.
When it gets time to cut it, just snip it in half using sharp scissors (it's very tough to cut and you don't want to saw through it..)
120 Gal SW, 150lbs Prem. Fiji, 23Gal Sump, 2x250w 15K MH, 4x65w Actinic
3 x Halichoeres Chrysus (1 surfed), 3 x Nemateleotris magnifica, 1 x Centropyge bicolor, 11 x Scarlet Hermits, 6 x Zebra Hermits, 40 x Astrea Snails, 6 x Nassarius Snails, 3 x Cerith Snails