Usually a halt is applied before an announcement to prevent illegal and overly speculative trades, if that announcement is percieved to influence the market significantly.
I am not aware of reasons for a halt after an announcement, unless the ASX has applied it for some reason (I am guessing). Are you asking "after an announcement" Chaka?
Thats my understanding, but others are probably better placed to answer.
Trading halts can also be a bit of a test to see how well u know the company, because if u have done your research you should have a pretty good idea of why the company has asked for a halt.
Yes the trading in the stock is suspended temporarily just before a company announcement. Can be good or bad depending on the market's reaction to the news.