Hotel WiFi networks are not as straight-forward as the wireless you have at home or at the office. As a result, you might not be able to send images from device to device via PhotoSync and WiFi.
In those situations, keep in mind that PhotoSync can also send photos to Dropbox. I can upload a file from one device or my computer to Dropbox, then grab it with another. It adds one extra step, but for those situations where direct transfer doesn't work, this method is a lifesaver.