In my classes and demonstrations I always tell people (in the U.S.) to register your drone. Even if it's only used for Recreational Flights, and under 250g. My reasons are two fold.
First, like above, if you end up over 250g by adding something, you're still legal.
But mainly I suggest people do because it's only $5, and if you are ever contacted by law enforcement, they expect to see a registration number. The <250g rule isn't always known by them. It's just not worth trying to explain it do them. Just register it and call it happy.
And if this isn't your first drone, then you should already have a registration number for your drones. So just put it on there. Make your life easier.
First, like above, if you end up over 250g by adding something, you're still legal.
But mainly I suggest people do because it's only $5, and if you are ever contacted by law enforcement, they expect to see a registration number. The <250g rule isn't always known by them. It's just not worth trying to explain it do them. Just register it and call it happy.
And if this isn't your first drone, then you should already have a registration number for your drones. So just put it on there. Make your life easier.