Who would you prefer when the shit hits the fan?
Cleric A: Just heals until oom, says "oom" and then sits down and prays the group gets out of trouble.
Cleric B: Already had root loaded, loads up stun... starts rooting adds between heals, stuns adds at full health to be root parked away from the action.
You'll find more Cleric B's will have solo'ed and know a thing or two about surviving the bad times
[You must be logged in to view images. Log in or Register.] So I'd recommend every cleric tries some solo, whether its early levels, spectres, hags, Kunark undead across many levels/zones there.