As far as I have ever used it, never. All it does it grab the content of the chunk specified, and just putting the chunk tags in will have the same effect.
Actually it does behave a bit differently. @CHUNK directly gets the content of the chunk from the database, while using the chunk tags just lets MODx get the chunk when it sees the tags in the TV’s output.
There might be conditions where the chunk tags won’t be processed by MODx, but it would be under very unusual circumstances. If your resource is getting passed through the parser more than 10 times and the chunk tags were only output by the TV in the 10th and last pass, then I suspect you’d have bigger design issues with the resource than that.
The parser will process the resource as long as the latest pass produced output different than the previous pass, or until it’s gone through 10 times. This is the default set in the main index.php file, line 118 -
$modx->maxParserPasses = 10; // max number of parser recursive loops or passes
So even if nothing else happens, the TV’s output of the chunk tags will cause another pass, where the chunk tags will get processed. So at most using @CHUNK will save one pass through the parser, and chances are the TV’s output wasn’t the only difference in the previous pass anyway.
Another use for @CHUNK might be if the chunk is being used as a parameter list for a snippet, and the TV is used to make a choice of chunks on a per-resource basis. In that case, using a TV in the parameter list might cause an issue if the TV’s output into the parameter list were just chunk tags rather than the contents of the chunk.
☆ A M B ☆