Uncle i agree it is both at all times.
TDS, i have had and seen such cramps for an example...
Things can need faster than anticipated reaction time.
Can lead to all sorts of problems.... is why i have been hesitant to go further in to more complex bondage at this time. sighs. but i'll get there........

I think it's all about the trust and deep communication.. if the two parties know each other and comfortable with their skills .. i think life has a way of working out from that point..... it's worked for me so far.