The question is a bit ambiguous making a straight answer a bit difficult to provide. This is mainly because Google Ads Smart Campaigns appeal differently to two sets of people namely 1) The Google Expert and 2) The Novice.
Having said this I will try to answer from both perspectives. Starting with the novice.
This figure shows the results of a smart campaign before it was adopted by an expert
For the novice, the merits of running a smart campaign out weigh the disadvantages. You will find that Google really went out of their way to provide an interface that is easily understood, anyone can create a campaign inside 10 minutes.
In the long run however the novice will start to notice that their campaign is not out performing competition and KPIs are really not what they desired. The end result will be the novice pausing their advert and seeking professional assistance.
In general for the Novice the pain is not in the interface or the use of the smart campaigns themselves. The pain is in the not getting the desired result after a budget has already been used up.
7 day performance time series showing clicks, impressions, ctr and average cost. [Meylic Digital Marketing]
From an expert’s point of view, everything about the smart campaigns is wrong. We want control, we want control on where the ads show, which keywords to use, how much to pay per keywords, What ad copy to use, Which report to generate, the list is endless
Performance in Google Ads is much superior.
As you can in the above image the expert has a much better control of the account evident with the performance results. Which is in direct contrast to what the smart campaign provides.
Smart campaign, simply do not provide desired results.
You will find that the Expert wants to adjust every part of the campaign to achieve better results.
Smart Campaigns are simply too narrow and do not provide the tools as expert requires to: