Should my family file be split into separate files based on ancestral lines? The answer is "This is a matter of opinion." Here are the pros and cons of creating more than one family file to record your ancestral lines.
PROS: If you have an extremely large family file with hundreds of thousands people, dividing your large file into smaller, more manageable files can make it easier to find and manage your data. When you send files to other people, the files will be more focused, rather than containing a lot of extra people they may not want.
An extremely large family file will also take longer (many hours in some cases) to do tasks like backing up, exporting, importing, file maintenance, etc. Also the maximum size for a Legacy family file is 2 GB (a little over one million individuals, give or take a few hundred thousand). When a file reaches the 2 GB limit, you cannot add more people to it. Any attempts to do so will probably result in corruption that cannot be repaired.
CONS: If you divide a family file along ancestral lines (for example father's father's line, father's mother's line, mother's father's line and mother's mother's line) you will not be able to create a pedigree chart or an ancestor report that contains all of your ancestral lines because any file you work from will be missing the other family lines.
One of our support techs says "I like to keep all of my family lines in one modestly large file because my pedigree charts and ancestor reports will have everyone. Also by doing this I have learned that my wife and I are 10th cousins, and that my step-brothers are my 8th cousins. I would not have learned this if I kept these lines in separate family files."