As per the lotg, you only need to use your whistle for a restart when it's a kick-off or a penalty kick, you show a card, there has been an injured player, a player has asked the ten yards, or there has been a substution. Off-side offences are dealt with an IFK, so no need to blow your whistle unless one of the above happen (quite unlikely, tbh).
However, it can be a tool if you want to hurry the things up a little bit. Imagine the team restarting game are leading 2-0 and there's 20 minutes left. I bet they'll take these situations quite easily. With no urge to restart at all. Two short whistles accompanied with an evident hand gesture should convey the message that your patience is wearing thin. And this should be enough warning for them to know that the next restart they take this way will end up in a yellow card that will come to the surprise of no one.
Key: edited text.