Question about Library Design

Hello,
 
Recently, I was looking at the source code for the SDF rendering portion of FreeType, and I was surprised to see that all the math is done using fixed point numbers. Looking further, the library does not use floating point at all. What are the primary reasons for this? Is it just a relic of the original library design when fixed point numbers were significantly than floating point numbers? Do they allow for slightly more precision when working at a certain scale? Are there separate compatibility reasons? I am sorry if there is an explanation somewhere on the FreeType website; I was not able to find anything. Thank you in advance for any explanation.