
In every team sport, each player has a role to play. Whenever a squad is picked, a team picks players according to how the roles they plan. In T20, if there is no clarity and distribution of roles then the team won't be able to sustain for a long time. Team Construction is an art and every IPL season gives us case studies on how teams build a team and what roles they give to players.
Spinners play a key role in T20, especially in India - they bowl the majority of the middle overs, the phase where most T20 matches can be won or lost depending on how a batting team performs. Powerplay(1-6) and slog overs(17-20) are the phases where batters look to attack the most but middle overs are a tricky phase.
In this season's IPL, most of the franchises took the defensive-offensive approach when it comes to giving roles to spinners. The defensive role meant that spinner will be the one whose role is to be economical from one end even if he doesn't pick wickets. The offensive spinner was the one who was given liberty to attack so as to pick wickets.