As an umpire, I always want to get the call right. I will always go to my partner for a discussion if there is even a remote possibility that he might have more information for me. I have no problem with a coach asking me to go for help on situations such as the following:
A pulled foot
A tag that was applied away from me, which my partner might have had a better angle
Here's an example from this past weekend. This is a classic example, IMO.
I'm BU with runner on 3B. Ground ball to F5, fielder checks the runner back to 3B and throws to 1B. Throw is high and F3 stretches. Ball beats the runner, and F3's foot never comes off the ground, so I call the out. 1st base coach requests that I go for help on a pulled foot. No problem. I talk with my partner, and indeed, while the toe never came off the ground, the heel did come away from the bag such that there was no contact with 1B. PU said it was pretty obvious from his angle, and he had no doubt. I overturned my call, and put the BR back on 1B. Fans that were sitting in left field weren't happy, but everyone else knew we ended up with the right call.
The issue becomes when a coach wants me to "go for help" on judgement calls, such as force plays or tag plays for which I am in the best position. I will not honor the coach's request in situations such as this. If I would, the door would be open for the coach to question every call, and that is just not good for game management.
ASAPAump's post offers two excellent spot on examples of situations when we do and when we do not go to our partner for help; and most importantly the reason why most times we do not honor the coach's request that we ask for help from our partner.