Why TrueType (TTF) and OpenType (OTF) fonts are recommended?

This page says you recommend TTF and OTF, can you tell me why?
I think Tor Browser was not affected by the font I installed.

I am using Whonix within QubesOS.
I use two different templates, the original whonix-ws template and whonix-ws-mylanguage which I changed to my language and installed input methods.
Do you think it is necessary to go that far from an expert’s point of view? Is it excessive?
I am not a computer or security trained person so I don’t know if what I am doing is right.