Iv seen posts with people substituting rape with r@pe. Other than bypassing filters I can’t see a reason to censor just 1 letter that doesn’t actually censor the word? I see if you fully censor the word, but even still context completely ruins the censorship.
It is to get around filters on more oppressive platforms. My recommendation is if you see people self censoring themselves in places where they are free to say the words, tell them to say it!