Starwood Preferred Guest (SPG) had partnerships in place with Delta, China Eastern, and Emirates while Marriott partnered only with United.
Marriott promptly ended the Delta tie-up, after buying Starwood, while China Eastern one lasted until May 2019 (read more here). The partnership with Emirates was relaunched in July 2019 (read more here), and Marriott and Emirates have sent out emails this week inviting members to sign up.
Marriott Bonvoy Platinum and higher members receive certain airport benefits while Emirates Skywards Gold and Platinum members some benefits while staying at Marriott hotels.
Marriott Gold and higher members receive 3 points per USD charged for Emirates flights while Skywards Silver and higher members receive one mile for every USD spent at Marriott hotels.
Marriott and Emirates members must link their accounts for the bonus miles/points and benefits. This assumes that it would make the most sense to credit the Emirates flights to Skywards (not who fly on Emirates infrequently).
Emirates elite members receive minimal benefits when staying at Marriott’s, while Bonvoy elites receive limited airport benefits when flying on Emirates. The most beneficial this is, however, for members who have elite status with both., You then earn bonus points and miles without having to do anything.
It makes sense for members to link their accounts, however, because there are occasional bonus opportunities for those who have signed up for the program.