Every ball is an event in the T20 format. For the batting team, every ball that didn't go for a boundary is one ball missed, and playing a dot ball is a win for the bowling team. While the batting team tries to maximise every ball, the bowling team just wants to bowl as many dots as possible.
The opener's job is very crucial at the top of the inning because those playing in the powerplay are selected to due to their skill to not only play the new ball but also smack it and utilise the fielding restrictions.
Bowling in this phase is quite tricky and bowling a spinner is always a risk. However, Derbyshire took the risk of bowling Mark Watt inside the powerplay during their match against Yorkshire in the T20 Blast and it turned out to be a jackpot.