We still use the Premier USB 1200 in some situations, even with the 3300... the reason is convenience and quality, it is super easy to change MOH in minutes by moving a flash drive from the unit, copying the file, then putting it back in, or having multiple files in rotation. Many customers don't like the fact they have to get the MP3 file from their vendor, convert it, then upload it, so they would rather get a digital MOH device that makes it easy. Plus the quality of the file based MOH in the 3300 kinda stinks, external MOH is much better in most cases.
So, to the OP, is it required... no. Might you want it anyway... maybe.