I have in the past does data extractions from systems which really can't serialise properly, where the only option is to concat all the fields with some "unlikely" string like @#~!$ as a separator, then pick it apart later. Ugh.
It's not doing just this, you pick something that's likely not in the data, and then escape things properly. When writing strings you can write a double quote within double quotes with \", and if you mean to type the designated escape character you just write it twice, \\.
The only reason you go for something likely not in the data is to keep things short and readable, but it's not impossible to deal with.
But some people (plenty in this thread) really do think "pick a delimiter that won't be in the data" - and then forget quoting and/or escaping - is a viable solution.