In practical terms while DDA does attribute conversions, it only does so with the Google ads ecosphere and doesn’t take into consideration how organic might play into things, for example.
I.e. In a 10 step conversion path that goes
Org > Org > Org > Org > brand ppc keyword > Org > Org > generic ppc keyword > Org > Org
Google ads conversion tracking would take credit for that conversion and DDA specifically would give you 0.5 conversions against the brand keyword and 0.5 against the generic.
(it’s been a while since I analysed DDA behaviour vs conversion path stuff but it kinda splits things that way from what I recall).
However, from that conversion path it’s difficult to argue that your ads had anything to do with the conversion.
Last click (imported from Google Analytics) wouldn’t give you that conversion at all, it would be given to organic instead.
Last click isn’t perfect, but it prevents you from getting overinflated conversion figures in your ppc account.