GMail displays a People Pane with sender and receiver email addresses on the right hand side of the conversation page. The People Pane also provides option for Chatting, Scheduling Meeting and Sending Email to the Group.
The people widget is by default enabled in GMail but if you are not planning to use this feature then you can turn it off and create more space for your conversation page. You can turn off the people pane using the option provided as part of GMail Mail Settings.
Click the Option icon and select Mail Settings from the menu list.
In the General Setting page, scroll down to People Widget section and select Hide the people widget radio option.