Basically, they c an be worthless because things change and are impossible to anticipate so you have to use your own judgement.

It does depend on the type and the department. In one job, I was able to rewrite the appraisals with clear descriptions of what was expected and, frankly, when they did those things, many other things did not go wrong and nothing big did. But it depends on the type of work. (We were forecasting sales so I would have them balance up where they thought they would be at the end of a specific time period and compare that to the results at the end of the same time period with a new months of sales under our belt. They then needed to account for the difference on a month by month way so errors or changes to trends were caught early).

But in most jobs it is not that easy to break down.

Add to that some managers have no business being managers so they tell you what you should do or do more of which is exactly what they do that makes them ineffective so there is that too. (Key lesson I learned is to get rid of those managers. By the time they are known to be trouble they have already done a lot of damage.)

Finally, a corollary to this is the damage that can be done when supervisors stick to the original plan at the end when outside events pulled people correctly off the work that was original agreed up because people will then learn to stick to the plan -- all to other organizational needs be damned. I also experienced this. I understand exactly why the people were doing it and could not blame them for not changing gears because management was truly the problem for holding them accountable to those specific set objectives and any deviation which could yield a much better organization result on another metric (not being measured) would not matter.

One last finally, I worked in product planning for a while and the net result of our work would not be truly determined a 2-3 years down the line. From experience and hindsight again, I was on a team that pushed to get the best product out there -- which can sometimes challenge executives and others involved. We pushed hard. Short term wise the effort was not valued or appreciated too much but, after some of us moved on and the product was released, the effort was recognized. (I say this as a member of the team that worked on Motor Trend Car of the Year, North American Car of the Year and just about ever other award given out that year to a car. I am glad I was part of the team and understand the work that went into it but I also saw later how some people floated and did not push and who were rewarded either for walking into an easy carline or for just agreeing with the status quo and pushing papers long. They were often rewarded because everything seemed fantastic -- and the real cost was realized later often when the problem they created fell into someone else's lap. They reaped the gain and not the loss while other got hit with the loss and not the gain. I did not understand the dynamic too much until I later when I moved into another department and worked with different planners and teams.)