That's not, in general, a very safe thing to do. You have no idea how long the session that you're killing has been running, you have no idea how important what it's doing is and you have no idea whether whatever it's doing is correctly using transactions or whether killing it part way through will leave the data in an incorrect state.

Basically, you could end up with really long rollbacks, you could end up killing very important processes, you could end up messing up the data if the people who wrote the code didn't use transactions properly.