I'd say it depends on how you plan to print them and research them. I have several projects going at once, and many have to do with following all of the descendants of particular families. If I want to print a family journal report on one family that intersects occasionally with a second family, I will keep them as two separate projects so that the printouts don't include several generations down the female lines of the other family that I don't want to include. I have another family for which I'm only including the barest information, but it intersects one where I keep extensive information. So there are times when I want to print a lot of details on some people and times when I don't. The program can do this for you but the searching and grouping is pretty complex and too difficult to run every time you want to do a printout. Whatever you decide, think carefully beforehand because it can be difficult either merge or separate them aftewards.