The option to choose between 1 to 20 titles and descriptions simply means that one could opt to have a website submitted to directories using 20 different titles and descriptions. These are automatically rotated on each submission. The benefit of such a feature is that, since it allows you the option of having multiple titles, it is essentially giving you the option to vary the link/anchor texts you'd like pointing to your site. When you choose to have multiple titles, you are targeting multiple keywords and key phrases with which your site can be classified.
It's always advisable to have as many titles and descriptions for the purpose of submissions.