The benefits of a high valour king and the regeneration of bodyguard units are indeed good points,
but it still only takes one lucky missile and your faction leader is toast.

Early on when the power of the RK is unmatched I will take my king in, but in high - late era there are too many troop types that eat armoured troops for breakfast so I leave him out.

I don't like the feeling from taking a general into battle but sitting him up the back of the field away from the heat.
If I am going to march him onto the field then he must be prepared to get into the fray or his place can be better filled by another troop (say 40 beautiful Chiv Kinights instead).