I take this question to be referring to the place of autobiography as a historical type of writing. In other words, do we need autobiographies less in writing history than we would once have done? I would say that we do need autobiography less than in times past.
The reason for this is that autobiography is no longer needed to get good insights into important people and important times in our history. Today, we have so many ways to get information about important people. The media are everywhere and so there are many sources of information (such as interviews) about people and their times. Nowadays, we no longer need autobiographies as important sources of information and insight into important people and their times.
This is a great question. I would say that the genre of autobiography is not less important today at all for a few reasons.
First, there is a real celebrity culture in America today. Through media, the proliferation of the Internet, and other social media outlets, people are divulging more of themselves to the public. Moreover, people are take it in with earnestness and zeal. In light of this, the market for autobiographies is rife.
Second, the intellectual and social climate is also amenable to autobiographies because of our postmodern sensibilities. For instance, there is a commonsense understanding that all people have a valid perspective. So, to read to read about the life of famous and significant people in their own words is in vogue.