Personally, I would not care about the trace flag at all and I don't understand why Microsoft bothered implementing it. The point with IDENTITY is that is a meaningless number which you at most can trust to be monotonically increasing. If you care about the values in it, you should not use IDENTITY values at all.

In any case, using the trace flag means that you will not get the benefit of the caching that was implemented in SQL 2012, and which can matter in scenarios with a high insert-ratio.