Use them, even if you might not be convinced of their safety value. Arguments have been made that safety chains don’t provide overall safety for motorcycle trailers but they are required by law in most states in the USA and provinces in Canada on the grounds of safety.
Hook up the safety chains.
Be sure the chains are crossed.
Part of your trailer inspection should be a drop test.
Un hook the hitch, but leave the chains attached.
Then drop the tongue so that the full tongue weight
impacts on the chains. The trailer tongue must not hit the
ground or be able to swing forward and touch the bike's tire.
The chains must hold. Don’t use light duty spring clips for
fastening the chains to the hitch rings. Keep the slack out
of the chains so the tongue doesn't dig into a pothole or
hit a railway track.
Snug the chain up as close as will still allow
the trailer to turn close to 90 degrees to each side.
Safety chains keep the bike and trailer together. They will keep your expensive trailer and its contents from bumping down the mountainside by itself, self destructing and perhaps taking out a car or another biker.
The trailer has to be in here somewhere!