Depends on the options you choose. If using conversations as the smart bid option CPA, then you need a history of conversions. The Call Rail API conversion import uses the Last Click Attribution Model,(you can’t edit that) and that may not be in your best interest as the conversion goal for smart bids. The GA import might be a better option with editing to a Data Driven (best) or Time decay attribution model.
Also with most smart bidding models the system includes some Google hosted conversion metrics that may not coincide with your ROI revenue or lead generation objectives. Such as GMB metrics of driving directions, etc. View your convesions tab in Google Ads to see what Google hosted events are automatically added.
In my experience, I have some campaigns that work great with smart bidding and others that manual bids are still the best.
Each campaign has its own goals, and the offer, budget, the USP, competition are factors in decision if smart bids are the way to go.
At this point 85 percent of all accounts and campaigns I run are still manual bidding as I out perfom all smart bidding. I may transfer the other smart campaigns back to manual as my data shows I always crush the API smart bid.
In conclusion think of this. To Google a conversion is a click, to most marketing people a conversion is a lead, but to an owner, the only conversion is a sale or when $$$ is received. Smart bidding plays to the first two more then the latter.
Hope that helps…