In brief
letter-spacing adds or removes space relative to natural character spacing. Positive values spread text out, while negative values tighten it.
Useful to know
letter-spacing adds or removes space relative to natural character spacing. Positive values spread text out, while negative values tighten it. [1]
A decorative heading and a long paragraph have different needs. Check complete words in the site's actual fonts; a rule that suits a short English label may make Bulgarian text uncomfortable to read.
Sources
For further detail and to check the information: