One mistake that many writers make is with commas. Some writers put too many commas while others do not put any commas at all. It is common for writers to put commas in all the wrong places before all the wrong words. The end result of such mistakes is badly constructed sentences that end up giving the content a shabby and unprofessional look. The placement of punctuations is important enough for every academic formatting style to have its own set of rules regarding it.
The APA style is no exception. They have a set of rules dedicated to commas as well. The style does not allow any commas between parts of a measurement. But writers can use this punctuation to separate lists, groups of three digits in a long number, and a reference in a parenthetical comment. There are some formats of dates where this punctuation can be used and other formats where they cannot. Writers would be well advised to read an APA manual to clarify how date formats are to be written. Invariably date formats that are written incorrectly act as the first pointer to the lack of professionalism on the part of a writer.
However, while writers can make mistakes with commas and perhaps even get away with it, editors and proofreaders do not have the same luxury. The manuscript ends up in their hands after the writer has prepared it and it is their job to make sure that the content is perfect in every sense. They should also ideally have a copy of the APA manual by their side so that they are aware of exactly how the commas are to be used. They need to go through the document very carefully because an incorrectly used punctuation has the capacity to alter the very meaning of the sentence.