Did you find it difficult to say it at the same speed backwards as well as forwards ?
The reason why you should know the musical alphabet backwards as well as forwards, also to be able to start and finish on any note is because songs will rarely start from an A note then continue up the musical alphabet. This would make a pretty boring song. You should be able to say the musical alphabet backwards as fast as you can forwards. No songs, except scales, go only up or only down the neck of the guitar or the musical alphabet.
Here are all the different ways you can say your musical alphabet, forwards and backwards.