What mahsamatman said as far as what you were asking about: RDM, EQM, COS bonus.

Plus there's more reasons not to book as a codeshare:

Having a UA code on the foreign carrier's flight is usually a negative:
- Difficulty getting seats in advance.
- Potential difficulty with changes and irrops while they try to find the PNR or e-ticket and get them back in sync.
- inability to upgrade LH flights with a UA paper SWU if coded as other than LH.

Unless you find significant cost savings from booking under the UA code, or you're required to book under the UA code from the "Fly America" act as a government employee, there is lots of downside and essentially zero upside for booking a foreign carrier flight under a UA code.

Note this is 100% the opposite of how the oneworld alliance works, in case you are familiar with that. In ow, the code matters. In *A, the metal matters. (there are rare exceptions to both, but this is the general case.)