You get a 10% bonus when you transfer your Marriott Bonvoy points to United MileagePlus for award miles. Normally points transfer at a 3:1 ratio, so 3,000 Bonvoy points will yield 1,000 MileagePlus miles.  But when transferring to United, you will get 1100 miles.

For Marriott Bonvoy Titanium Elite and Ambassador Elite members–

These members are eligible to register for United MileagePlus Premier Silver Status. Register now.

For United MileagePlus members who are Premier Silver or higher 

You can convert your MileagePlus miles into Marriott Bonvoy points at a 1-to-1 ratio, up to 50,000 miles yearly.

For United MileagePlus members who are Premier Gold or higher 

You get complimentary Marriott Bonvoy Gold Elite status.