No information will be lost. In the upper portion of the profile (birth dates, places, etc.) if there's only one piece of information it is used. If both profiles have that data then you get to pick which data is used ... it's color coded, green and orange I think. In the Biography section, both sets of data are placed into that area, one of them first and the other second. So. after the merge, you need to edit the Biography/Sources section and make it look spiffy again.