If your home directory is private, then no one else can access any of your files. In order to access a file, a process needs to have execute permission to all the directories on the path down the tree from the root directory. For example, to allow other users to read
/home/martin/public/readme, the directories
/home/martin/public all need to have the permissions
d??x??x??x (it can be
drwx--x--x or some other combination), and additionally the file
readme must be publicly readable (
It is common to have home directories with mode
drwxr-xr-x (755) or at least
drwx--x--x (711). Mode 711 (only execute permission) on a directory allows others to access a file in that directory if they know its name, but not to list the content of the directory. Under that home directory, create public and private subdirectories as desired.
If you never, ever want other people to read any of your files, you can make your home directory
drwx------ (700). If you do that, you don't need to protect your files individually. This won't break anything other than the ability of other people to read your file.
One common thing that may break, because it's an instance of other people reading your files, is if you have a directory such as
~/www which contains your web page. Depending on the web server's configuration, this directory may need to be world-readable.
You can change the default permissions for the files you create by setting the umask value in your
.profile. The umask is the complement of the maximal permissions of a file. Common values include 022 (writable only by the owner, readable and executable by everyone), 077 (access only by the owner), and 002 (like 022, but also group-writable). These are maximal permissions: applications can set more restrictive permissions, for example most files end up non-executable because the application that created them didn't set the execute permission bits when creating the file.