I may be wrong but my guess is it's for items you've bought that weren't solely for yourself. If you bought two pairs of gloves from Ebay but one pair was for a friend, the "Split this" would send your friend a request to PayPal you back 50% of the cost.
"Split This" is just another in a long long list of useless social engineering schemes that they actually pay millenials to dream up for our "perfect utopian world". Ha ha, get used to it.
As I understand it I can buy something and have all my friends pay for it. Some deal!! The PayPal person who thought this up doesn't know what they are doing or they don't live in the real world.
