I can’t recall reading this in the curriculum; only reason I can think of is that if you overestimate goodwill, this is equivalent to an underestimate of the assets of the target company. So instead of valuing the acquired PPE as $ 120, you set it to a value of $ 100. This results in a lower (additional) depreciation expense and hence higher future profits.
Though this would increase the likelihood of a future impairment of the goodwill.