WSPR signals propagate around the world and allow very weak signals to be correctly decoded. WSPR is some 12-14dB better than normal speed CW. If 10W gets through on CW less than 1W is quite enough with WSPR. My own 10m 500mW beacon, to a simple "nothing special" end-fed wire antenna has been copied on every continent in recent weeks, including Australasia and Antarctica.
The main bonus with WSPR is that all reports can be automatically sent to an internet database (WSPRnet), so anyone can see where signals are reaching and how well. Today though, the WSPRnet database has been in trouble, possibly due to being overloaded. It was not working the last time I checked but was working late this morning.