Strengths

They will keep your strongest units alive relatively easy. Giants and PEKKA will last so much longer with a healer behind them.

Weaknesses

They are very vulnerable to air defenses.

They cannot heal flying units unfortunately.

They also cannot do anything in battle besides healing.

Tips

Make sure you clear out any air defense so your healer won’t get targeted.

Healer and Giants make a good combo for making your “meat shield” withstand more tower attacks.

Battles will end even if your remaining survivors are healers.