On even somewhat simple flies, it’s kind of remarkable how many times in the tying process you end up using your primary tying scissors to cut or trim materials, both on and off the fly. So, it makes sense, wherever possible, to keep the scissors in your hand rather than continually putting them down on your tying table and picking them up again.
Having the right scissors to do this is important but has a lot to do with your hand and finger size as well as your tying style. For me, I like relatively short scissors with fairly large finger holes. These allow me to palm the scissors while I’m manipulating materials then quickly switch to trim materials then back to handling them again. Some tyers prefer spring-loaded scissors for keeping in their hand while they tie, as opposed to regular.
It’s also important to be able to simultaneously hold and use other tools along with your scissors, like a bodkin or even a whip finish tool. Once you’ve completed a whip finish, your scissors are already in hand to snip your tying thread free.