Yes! FDM printers need to be enclosed !!
Research is showing that as the plastic comes out of the extruder, there is a fine mist of plastic particles expelled into the air. An enclosure will contain this. I would also FILTER the air in the enclosure of the printer too once printing is done.

Also, an enclosure will keep the air hot around the print job substantially reducing the likelihood of the print disconnecting from the base plate. This will increase the success rate of your print jobs.