Honestly, I can't see Spock dropping his katra into someone else every time he planned on doing something dangerous.
Agreed. And I think people need to keep something in mind. When Spock gave his katra
to McCoy in TWOK, he knew
he was going to die. He'd already made the decision to sacrifice himself to save the Enterprise
while on the bridge (you can see him pause just before he leaves his station). Transferring the katra
to McCoy was his way of closing the loop. It's not something he would do every time he entered into a dangerous situation.