An MC-LAG provides
- redundancy and
- load balancing between the two MC-LAG peers,
- multihoming support, and
- a loop-free Layer 2 network without running Spanning Tree Protocol (STP).
Chapter 3: Next-Generation Internet Exchange Architecture Case Study
Hashing algorithm for link aggregation groups (LAGs) on EX Series switches
https://kb.juniper.net/InfoCenter/index?page=content&id=KB22943&actp=METADATA