Re: Why Pay Pal... ?
I don't believe I've ever had a chargeback, so I can't speak from experience at that end. But if you use PayPal to pay by credit card, and it appears on your bill, it's just like any other transaction. You can query it with your card company, and I would imagine that if you declare it to be fraudulent, they will do a chargeback, and the consumer doesn't end up out of pocket. From the point of view of the consumer, the only difference is that they merchant that has actually charged their card is PayPal (and if you donated to one of my sites using your card, it would appear as "PayPal *Nigel" on your statement.
So, no difference in consumer protection at that end of things (there will, of course, be slightly different rules if you pay using a PayPal balance).
A quick skim of the help suggests that PayPal leave it up to the credit card company to decide if the chargeback should happen; the merchant may (depending on whether it's something with seller protection or not) take a hit of the original amount, plus £14 processing fee.
So, pay by card via PayPal (where all they're really doing is acting as a card processor without requiring upfront fees from the merchant) and you have exactly the same protection as using a card anywhere else.
Pay using a PayPal account, and you're subject to the usual PayPal rules, and their own quirky interpretation of them.
In terms of how it helps the buyer, I suppose that's really just that it makes it easier for some people to provide a way for you to give them money that doesn't involve putting cheques in the post. A lot of people will be far more likely to give to something, whether it's one of my websites, or a cloud funding type of thing, if they can simply use the 'normal' way of paying, which is credit card. So, yes, the convenience is mostly for the seller/fundraiser, but being able to process cards does make life simpler, and the process more understandable, for a proportion of customers/donors