By default, Photoshop uses fractional character widths, which helps the spacing between letters. However, when you’re using any font to be viewed online below 20 points in size, the type can run together or have too much space. You can turn this feature off, but it affects the entire text layer; you can’t apply it to just part of the text. To turn it off, choose System Layout from the Character panel’s flyout menu. To turn it back on, choose Fractional Widths.
by Pete Collins