Pyro's come in two main categories. Smoke grenades and flash bangs.
Smoke Grenades or Smoke Bombs as they are also know as, are used to create a smoke cloud, to hide your movement in the game. Throw a smoke grenade between you and the opposition to obstruct their veiw and conceal yourself and your fellow team mates.
Paintball and Airsoft skrmishing isn't the only use for smoke grenades, they can be used for so much more.
Photography - Create clouds of coloured smoke for some amazing effects.
Events - Add colour to your outdoor events
Weddings - Always somewhere within a wedding for someone to use a smoke grenade
Gender Reveal - More and more often, couples are using coloured smoke grenades to gender reveal.