Now you can have any number of tar files. There is no limit. But beware of using too much disk space because every file in the directory is copied into the tar file. Sometimes you only want to extract one file or just one subdirectory. You can use tar for keeping files together, not just for compressing.
Lots of data is stored on computer systems as compressed tar files.
In other words, someone has bundled together a directory of files into one archive, and then compressed it. If there are compressed files already in the directory, this process will not hurt them. You can have any kind of files inside that directory, even other tar files, even other compressed tar files. However, tar files and compressed files contain binary codes which are unreadable and may screw up the mail system. There is a program that can create a readable file from an unreadable one so that it can be sent via email.