Microsoft's Your Phone app might soon let you copy and paste from one device to another. The app, which is designed to bridge your PC with your phone, has hints of this feature in its latest Insider version. Some references describe a new Content Transfer feature. It has the references like 'SharedContentPhotos,' 'ContentTransferCopyPaste,' and 'ContentTransferDragDrop.'
Trying to enable the feature with a hack show the "Cross-device copy and paste" option you see above. But the feature doesn't seem to be live yet. It will be a useful one if Microsoft decides to enable it. Your Phone is available in the Microsoft Store, Google Play Store, and Apple App Store.
Source: MSPowerUser