Depends on the gear level and the instance. The continuum spans from the following:

Resto shaman heals full time

Resto shaman can help DPS and toss the occasional heal

Resto shaman is gone, and you run 4xElementals who can 4xLHW or 4xChain Heal occasionally to take care of damage

4xElementals with some healing streams and passive tank healing is enough to handle all damage


etc

It just depends on how challenging the content is and your relative gear level.