It would be fun to order your favorite fictional character around. Imagine having Riker as your Digital assistant and saying "Make it so, Number One" (or whatever your punny variant of that is) ... or any number of other fun characters to order around.
And of course a persona is more than the pure voice, but also writing and how they use their voice to say things.
EDIT: an article about Siri's voice actor: https://www.vox.com/2015/6/23/8831131/siri-voiceover-susan-b...
> "I recorded four hours a day, five days a week for the month of July," […]
> The goal is to try to include every possible sound (usually drawn from a syllable-long building block) so they can be assembled in every possible combination for every possible word. To record these, voice actors are forced to recite gibberish-like sentences that include all of the English language's different sounds […] including absurd phrases like "oil your mills jewel weed today."