This is a matter of opinion. Here are the pros and cons of creating more than one family file to record your family 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. You should also split your family file as it nears the 2 GB size limit. Once a family file reaches 2 GB no additional people can be added to it and you won't be able to split it.
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 for yourself because any file you work from will be missing the other family lines.
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, once removed, and that my step-brothers are my 8th cousins, 3 times removed. I would not have learned this if I kept these lines in separate family files.