A ceiling rose/canopy is an optional feature but is recommended to give your light fitting a neat installation to plaster ceilings. Where an electrical connection to mains is above a ceiling surface then a ceiling rose/canopy must be installed so that tension is removed from that electrical connection.
For all 240 Volt countries this connection can be via standard connectors or our Wago hardware either just in a ceiling cavity loose or inside a junction box where access is possible from above after installation.
For US/Canada all mains connections via wall or ceiling require a J-Box to be fitted flush. These require a specific canopy that will then attach to the open face of the J-Box.