I am very excited to see that Chase just added JetBlue as their newest transfer partner. While it might not provide one of the best values compared to some of the other airlines, it is an airline that everyone loves and to have another US airline to transfer your points to is great! 
Points transfer as a 1:1 ratio which is much better then the Amex Membership Rewards or Citi ThankYou Rewards programs rates and you do not have to pay any fees to transfer your points. JetBlue points are typically worth 1.4 cents per point due to their variable pricing, so the most the flight cost, the more points required for a free flight. While you typically will get a better “value” when redeeming on an international business or first class seat, those types of redemptions are not for everyone. I actually am one who doesn’t redeem my points to sit up front as I do not want to waste my points and prefer to stretch my points out as far as possible. Although, when it comes to Chase Ultimate Reward points I do prefer to get a minimum of at least 2 cents per point value.
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You can straight up buy jetblue tickets on the Chase portal for 1.5 cents per point (and you’d earn miles o that flight), so there’s no situation in which transferring to JetBlue makes any sense.
While generally buying through the portal for 1.5 cents would make more sense, there are some situations where it may be advantageous to transfer:
* I have the JetBlue mastercard that gives me 10% of my points back whenever I redeem them
* JetBlue sometimes (like right now) has discounts when redeeming with TrueBlue points
* It might be worth topping off a small number of points to use up an existing TrueBlue balance rather than using UR to pay for the whole fare.