last click assigns all credit to the last search ad clicked before conversion, while a 'data-driven' attribution assigns it to all touchpoints, assuming you have several search ad click touchpoints before the conversion finally happens.
this will impact your attribution but not to the extent you need to be worried about. for all its worth this new approach is certainly better than just last click but i would anyways recommend to not use google's own attribution as it is siloed, capture all touchpoints in your marketing automation platform and then create an attribution model that works for you and works across all your marketing touchpoints and not just google.
let me know if i can be more clear.