Quite often the consultant is hired because the client already knows what they need to do, they just did not know how to get it done or in some cases could not risk the political capital. Lean consultants don't get hired unless the client already knew they were running "fat". HR consultants often get hired because the management does not have the fortitude or strength of will to do the onerous head-chopping that the "efficiency experts" will eventually proffer as a solution.
As a Techni-HO you are often sought out because you are an outsider, you are not mired in the details for the day-to-day business and will have hopefully the insight to see what people in the company have blinded themselves to and to follow through with relatively distasteful action. You are the hired gun, there to do the job that they themselves won't do.
A manager at one of my contracts once told me--very insightfully--that he appreciated that we were there since we paid attention to the details and the follow through that they for purposes of self preservation did not like to bring to light. We had the dirty job of recognizing potential for growth in their process (which if they admitted it would have appeared to be weaknesses in their process).
Too often the voice of the outsider is feared by the in-house staff, they were threatened by our presence and undermined us at nearly every turn, but when it became clear that we would carry these unpopular messages to the forefront and champion their cause we found unlikely allies.
The story I hear often is this "a consultant is hired to tell the manager what time it is in the plant. The consultant walks around the plant checking everybody else's watches takes the readings and then communicates that time back to manager." Many who hear this story think, "how stupid, why did not the manager just do that himself?". The answer to that is if the manager did, he would immediately appear weak in front of his people. He would seem poorly informed, and when he declared the time many whose watches did not correlate would be angry that he did not take their word for it.
Instead by hiring the consultant to do the tedious data collect and present an answer, he removed that risk from himself. He also gained the benefit of an expendable resource he could turn on if the number was not correct (for this reason he could not require this task of one of his internal resources). Techni-HOs serve a purpose they are the needed muckrakers that every world needs but many are unwilling to admit they need.