For all I've always been against FR, I think for somewhere like NCL (mostly low yield when it comes to leisure), that, as FR says, high frequency and low cost may work on some routes. EZY doesn't always have the extremely low fares and LS doesn't always offer the frequency.
Think of somewhere like Krakow for example, x4-5 weekly at £30 return will probably work better then x2 weekly at £70+
... Providing the market is allowed to mature...