The font takes only 2 bytes of bitmap storage per character, fitting the entire character set into 196 bytes (assuming you only use the 7 bit ascii characters up to 7E), or 198 bytes if you store the space character as an empty bitmap in memory instead of as a hardwired/coded empty space.  It is not the smallest possible font, I have seen a 3x3 font, but this is extremely readable with the only questionable characters being the & and #, as there just isn't enough character width to fit the voids and loops, so the & can be possibly be mistaken for an 8, and the # only has a single vertical line.  But, monospaced this only takes 4 pixels of space per character on the screen, and you can fit 32 characters on a 128 pixel wide screen.  

character cells are 4x6, the character bitmaps are all only 3x5, which makes each character bitmap only have 15 pixels, fitting neatly in 2 bytes each.  

A 64x32 pixel screen has 16 characters per line, and 5 lines, with 2 extra rows of pixels unused.  A 128x32 display can have 32 characters on 5 lines.  compare this to a 5x7 font, where you can have only 4 lines and 21 characters per line.  

This is intended for retro computers or microcontroller displays where you want to squeeze more text onto a small screen, or you want to squeeze your ascii bitmap into less memory.  A 5x7 font takes 35 bits per bitmap, this takes 15.  A 5x7 font takes 490 bytes of memory, compared to 196.  in tiny hardware where you are dealing with single digit KB of memory, this might be very useful.