Nicotine shots are unflavoured, concentrated amounts of nicotine which is meant to increase the nicotine strength of your vape juice.
Shortfill E-liquids, the 0mg E-juices that are supplied in bottles with enough space, are used with Nicotine shots. The empty space in the bottle is filled with nic shots until the preferred blend of nicotine strength is reached. It can also be used for discreet vaping by topping up on nicotine or diluting a juice.
Though not used individually, nic shots are essential for vapers who wish to enhance their overall smoking experience.