Pool swim tri question

Here is a question for all you experienced triathletes.  I was thinking about signing up for a tri in May that starts with a 400 yard pool swim.  I think there are something like 11 lanes available for swimming.  So 22 swimmers will start, swimming in split lanes.  Swimmers stay in their own half of the lane and there will be lap counters.  There are going to be wave starts every 15 minutes.  Participants are suppose to give a predicted swim time when they register and waves will be based on that predicted swim time.

So my question is ....  Why would the race director care about how fast someone swims when there will be no conflict in the pool?  I have several theories, but really I am clueless.  Here are my theories:

1.  Start the faster swimmers in the earlier waves because they are going to be the most competitive and they won't have to worry about getting around slower racers in the bike and run portion.

2. Start the slower swimmers first so that everyone finishes closer together and you don't have to wait all day for the slower people to finish and get to the awards ceremony.

3. Each waves starts with a mix of faster and slower swimmers so that T1 is not very congested.

I'm sure there are other scenarios.  But could someone explain what the real reason would be for wave starts based on predicted swim times in a split lane type swim?

Thanks!  Diane