Index attributes selection

if i have a bucket called patients and i perform some queries on it and another bucket
what is the difference if i create the two indeces

CREATE INDEX idx2 ON patients(encounter,LAST_NAME,FIRST_NAME)
CREATE INDEX patient ON patients(encounter)
or it better to create idx2 only
primary index was created before

does it impact query and system performance

https://index-advisor.couchbase.com/indexadvisor/#1