A big advantage of this is that current individual transactions that sometimes won't go through (because they are a bit above the median due to many outputs (e.g. dust), or the daemon / MyMonero rejects them for some reason) can easily be included in the block without incurring a penalty. Above is a bit of a blunt explanation, I am sure one of the core-team members / developers could give you a more detailed explanation.
Finally, the recommendations from the MRL team stated in MRL-0004, of which the minimum mixin >= 3 is probably the most salient. See:
P.S. Due to variance the hard fork will likely be on the 21th or 22th of March. A specific block height was determined for the hardfork, not a specific date. The specific blockheight for the hardfork can be found here: