If the worst happened, how quickly could you get yourself and your playmate to safety, or release them in an emergency? It's a very good idea to have some means of cutting rope safely for such occasions. I suggest always keeping that in the same place so you always know where it is and you could find it even in the dark if need be.
I do NOT suggest something like this [shows blade]. If you need to remove rope from somebody who's panicking or having a fit, it's a very bad idea. EMT shears, or emergency shears, have a blunt flat tip to allow them to be slipped under rope without injury whilst the serrated blade means to rope can be cut in one snip.
Any of the problems in this section could occur, and with no means of escape, the consequences could be damaging or lethal. Of course this is a very good reason not to tie someone up and leave them, even for very short periods.