There are many different ways to finish in darts, some of which you may not agree with and can cause discussion among players.  

The main reason for many of the less traditional outshots, is to maximise the opportunity to checkout using the 3 darts in hand.  

One example is 80, I have seen many people go for T16 first. By going for T20 first, if a single 20 is hit, there is still a chance to finish with another Single number which statistically would be easier to hit than the 14 or treble required to leave an alternate finish. 
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