I have seen a lot of questions that uses abbreviations, like "idk", "u", "imo", as well as some short forms of site names like "SO". I tend to edit them to full forms when I see any, as I feel that it makes the questions' or answers' quality bad. But sometimes when some words are necessarily repeated (for example, "FAQ" and "SO" in this question), changing all the abbreviations into full forms make the question hard to read.
Should the abbreviations and short form words be avoided to be used at all times, or are they allowed at any times?