As far as I know, one needs to use double or single quotes for fonts if they contain spaces, like:
font-family: \"Times New Roman\", Times;
font-family: \'T
I've just learned myself that the quotes aren't ever necessary but rather recommended. We all learn something new every day.
The other place you see them is in css properties that require a url
background:url('hithere.jpg');
background:url(hithere.jpg);
Both those statements are going to work exactly the same. Same goes for the fonts, which type of quote you use is irrelevant in this case, just be consistent in how YOU do things and that is all that really matters.