Unfortunately, human nature tries to avoid the possibility of mistakes and excessive durations are an easy way to try to make sure of hitting or beating deadlines.
This techniques may appear rather attractive at first.
However, if you constantly achieve targets early, for example, this may be a sign of overestimation and you may find the manager doesn’t accept future estimates.
The other problem is, if there is a culture of overestimation and the manager is asked to cut costs he or she will be quite happy to reduce durations knowing there was probably ‘fat’ in the estimate any way.
Then, if you do start to produce realistic durations they could then be cut affording tasks that will not complete on schedule.
Note that some tasks finish earlier than expected and dependent tasks may still not be able to begin at this earlier time if they are dependent on other aspects.
Overly concerned due to lack of experience
It may be the individual is over cautious because of lack of experience.
If this is the case try to get estimates by involving a few people with the necessary experience to obtain realistic durations and resource estimates.
Delivering an over-engineered solution
This is a symptom of not knowing the requirements of the person that will use the output of the task.
Produce what is required and agreed and no more.
Be ware of the scope.
Over engineering could bring unforeseen problems and actually result in delays and potentially extra costs.
So, know what the deliverables are for the task.