i don't see why throwing a sword to a friend is any different than throwing a flask of acid or a dagger at an enemy, both of which are actions.
Ever played basketball?
If you shoot at the basket, you normally take an Action to do so, and even then you need to roll to hit; if you don't take an Action, your odds of scoring a basket are slim.
If you take an Action to pass the ball, then you'll send a catchable pass. (If someone tries to intercept, that's an opposed roll, so roll to see exactly how well you passed.)
If you pass the ball, but your main effort is on some other task (such as Dash), then you're doing that other task as your Action, and you pass the ball as an incidental action. You still have some chance of success, especially if the receiver makes extra effort to catch the sloppy pass.
Back to D&D: if you have the only magic weapon in the party, and you attack the foe and then toss the +1 sword to an ally, the toss is an incidental action, and it might not be easy for your ally to catch the sword well enough for them to also attack with it in the same round. Some of us say that's easy, no problem. Not at my table!
