The type of font in anything is very important and can have a massive impact on the message you are trying to give. you can set a mood just by using a different font. Changing the font, colour, size is also very important.
There are two different types of fonts, sans serif fonts and serif fonts.
Serifs are semi-structural details on the ends of some of the strokes that make up letters and symbols
A sans-serif font is one that does not have the small features called "serifs" at the end of strokes.
I watched the opening title sequence to “sev7en.” They used serif fonts to make it a lot less formal. The font was very effective, it almost makes you feel uneasy. This scruffy writing makes us aware that its going to be a rough film and its going to have a lot of quick sharp shots and its probably going to have death. The font also flashes a lot like lightbulbs which always indicates in films that something bad is going to happen.