On a recent project I had to migrate a large number of documents from a legacy system into SharePoint. In the old system users to choose what text would be displayed as the link. In most cases users chose not to use the actual file name as the link text.
In SharePoint users don’t have as much control of what gets displayed. There is a ‘Title’ field but it can’t be used in a calculated column and on the standard document library it is not a required field.
Technically the file name could be used but this could lead to very long file names with spaces and special characters that could cause problems by forcing the page to scroll as well as creating some REALLY long URLs.
Depending on the type of document the actual file name may be irrelevant to the use while the title would be more helpful. For instance a in document library of meeting minutes the file names could just be the date of the meeting for example (12_03_2009.docx). The document title could be used to contain not only the date but other relevant information about the meeting like who attended or important issues that were discussed. Additionally the title field can support special characters and spaces that could be a problem in file names.