Should you release music using the 'pay what you want' pricing mechanic or even for free? Is it worth doing? Does it help build a large audience? Does it help build more sales down the line? The answer is a resounding yes! I am absolutely an advocate of pay what you want, and also an advocate of releasing tracks for free to help grow your fanbase, get more exposure, and all of that kind of good stuff!
Bandcamp is the best place to release material pay what you want, but that doesn't mean you exclusively have to release it there. Yes, you have to fit within the pricing guidelines of other platforms like iTunes, but as long as you make your fans aware that your material is available for PYWY on Bandcamp, it's fine for it to also be in other popular places. You could consider having the material exclusively available as PYWY on Bandcamp during the launch period (say, one month), and then distributing it across the other platforms after.
Financially you should find that the amount of money you make will work out to be the same as, or better than, the amount of money you make if you had just charged the standard price for the material.
One of the great things about PWYW psychologically is that nobody can really be unhappy with the amount they have paid for your material. They independently put their own value on your music and that's how much they pay. It's hard to be unhappy with that. It's a very modern approach, and it works if you do right. You're basically letting your audience decide what your music is worth. To a lot of us that can be scary. You might be thinking "what if nobody thinks it's worth anything and we don't make any money off of it?!", which is a completely understandable fear to have! But if it's good music and if you are nice people, and particularly if you are reaching out and engaging with your fans on social media, then people will recognise that you're genuine and working hard, and they'll be happy to pay for your muisc. Some people might only pay £1, but some people might pay £10 or more! It tends to balance out on the whole, and it the value is in the powerful message it gives to your fans where you are essentially saying "we value you as fans and we think you should set your own price".