As @8orange8@lemm.ee said (https://lemmy.ml/comment/3459977), I believe they have different use cases. The TL;DR is: syncthing to have the same copy of a file across different devices, LocalSend to move files between devices directly.
On syncthing you have to upload the file to the synced folder and then download the file to your device, so like device A -> server -> device B.
Whereas on LocalSend you send the file directly between the devices, like device A -> device B.
As @8orange8@lemm.ee said (https://lemmy.ml/comment/3459977), I believe they have different use cases. The TL;DR is: syncthing to have the same copy of a file across different devices, LocalSend to move files between devices directly.
On syncthing you have to upload the file to the synced folder and then download the file to your device, so like
device A -> server -> device B.Whereas on LocalSend you send the file directly between the devices, like
device A -> device B.