Despite the promised travel facilitation, civil rights activists and data protectionists are urgently warning against the consequences of digitizing travel documents. They see it as an expansion of the biometric surveillance infrastructure at the EU level. The digital travel app initially provides for automated facial recognition for biometric identification, but it is likely to pave the way for comprehensive and automated collection and evaluation of biometric data. This would restrict freedom of travel in the long term.
Same as with banking. It's "optional", but eventually not really.
like buying software and not agreeing to the EULA.