Well, there's the satisfaction of helping the "underdog" (no disrespect intended!) against the big boys'n'girls. It helps that, in my experience, the underdog is also better! 

Or the fairness in paying for a service that we use.

I believe that subscribers have access to more map choice (the hamburger type menu on the top right of the map) as well as the ability to prepare PDF maps that are longer than for non-subscribers. 

Subscribers were invited to test out the app before release. 

Off the top of my head, I can't think of any more. 

My understanding is that CT operates on the notion of goodwill. If you think it's useful then throw a few bob into the kitty. It has been noted a few times on these pages that CT doesn't like charging, preferring to leave it voluntary. I think I'm right in saying that PDF maps are subscriber only because of the cost of generating such features. And those extra maps have costs and use up space. 

I'd encourage anyone who uses CT regularly and who can afford it to subscribe. Every upgrade in server space is a long term commitment and risk for them and every tweak, adjustment and improvement on the operation of the site/app is someone's labour. 

CT has brought me to some wonderful places. And never tried to kill me - unlike some other route planners! :-) That's got to be worth something! 

The difference between coffee, cake and beer is (with one exception) just the cost – it’s absolutely up to you how much you think it’s worth. It is all very much appreciated no matter how much, so thank you. The one exception is that beer and cake supporters have their names listed on the supporters page, which is linked from the cycle.travel page footer!