Ways of implementing MPC

[jargal]

I read on a github conversation that
"Bitcore [...] had a mostly functioning implementation of MPC that used P2SH and bitcoinj used raw multisig. These are not compatible, so I made bitcoinj's MPC into a P2SH version and modified bitcore's conversation structure to make them compatible" (from an experienced developer).
I thought I knew what MPC and P2SH were but I was not aware until now that MPC had been implemented in two ways, raw vs. P2SH. I ld like to more about this.

Could someone explicit the reason for taking one approach or the other please (or redirect me to some useful resource)?

Thanks