While Google Ads (and the few other ad services) imported data doesn't include VAT, most non-Google services data does. Thus, for the accurate analysis of comparable metrics from all your ad services, all the costs must be without VAT.
The standard integration with Google Ads imports cost data not including VAT.
- 10USD of campaign costs,
- 12USD charged including VAT,
- Google Analytics report shows total costs 10USD.
For non-Google services like Facebook, Specify the percentage of VAT in the pipeline settings (VAT rate in Google Ads may be different from VAT rate in Facebook) to import a proportional amount of Facebook costs.
If you don't consider VAT while importing cost data, you'll end up overestimate the costs of non-Google campaign.
As the result, you won't be able to make correct conclusions on the efficiency of campaigns, e.g. redistribute the advertising budget in favor of a campaign with lower ROAS.