I think I'm selling mine when they go under 400$, which I hope will never happen, but might even happen today the way it's going down now.
On the other side I think I will sell them at around 900$
I sell btc when I need money
it's easy no stress and when I do a change it means I need the cash

i also sell my bitcoins only if i need money really bad, though i always try to hold my bitcoins if possible in order to make as much profit as possible in the future