There are two main benefits to splitting your seed this way
The Multishard requires that you keep a redundant backup which means that even if one shard is lost or destroyed, you have others to rely on.
2. Exposure Resistance
One threat no single whole-seed backup can really protect you from is seed exposure (when someone finds your backup and now knows the entire recovery phrase). With the Multishard, you are not only protected from environmental threats like fires and floods, but also human attacks on your coins. Finding a shard is not the same as finding your seed.