Cork stoppers with a plastic cap (capsulated cork stoppers)  are  used to secure certain kinds of liquor like port, madiera,  sherry and fortified wines,  as well as Brandy,  Whisky and  Vodka which are all ready for consumption.  Capsulated cork stoppers are not suitable for long term storage. (unless sealed with wax)   They can be useful for resealing bottles whose contents are not used at one go.