Look, I get it: If you had to read briefs for a living, you'd want the parties to use typefaces that were as easy on the eyes as possible. Lord knows, lawyers' prose can be sludgy and kludgy and frequently is; if it at least looks good, however, it might be easier to wade through.
So, non-lawyers, restrain your snickers about persnickety judges in snobby D.C.
Besides, the D.C. Circuit judges are not alone on this. Take a look at pp. 170-177 of the 7th Circuit Practitioner's Handbook for Appeals (excerpt from Ch. XXIII: "You can improve your chances by making your briefs typographically superior"). The Illinois Courts area a bit more laid back---probably the difference between having life tenure and having to face retention elections, even if only once a decade---but Supreme Court Rule 341(a) still specifies that briefs must be double-spaced, in 12 pt. type or larger. Condensed type is verboten, and particular margins are specified.
But the D.C. Court's March 16 announcement is remarkable because the Court has singled out Garamond as a font to be avoided:
Certain typefaces can be easier to read, such as Century and Times New Roman. The Court encourages the use of these typefaces. Briefs that use Garamond as the typeface can be more difficult to read and the use of this typeface is discouraged.
Somebody over there really doesn't like Garamond....