While this season is Tier 10 across all the Leagues, other seasons aren't always set up that way.
The "Qualification" period is a good way to let people know, "If you do this you'll go to the next League and not be able to drop back down." Some folks liked to stay at Tier 6 in Bronze, or Tier 8 in Silver.
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You don't have to go for Gold~
Find the League that you enjoy the most! It'll refresh every 2 weeks during the current Season.