Copying on selection isn't everyone's cup of tea, and it causes clipboard issues in current builds of XChat (for Windows at least, 2.8.7f and below) wherein clicking in the text box without selecting anything clears the clipboard entirely.
This is annoying.
A right-click menu for copying text, and an option to disable copy-on-selection, would be fantastic. I know it's possible because the XChat text box currently maintains and tracks your selection even after it has been copied. This is pointless.