1. licensing voice to other uses - people with recognizable trademarkable voices (actors, singers) have another potential revenue stream. yay!
2. use of past voices - voices that are not 'owned' from the past - let's say Humphrey Bogart's voice, can be used in projects without having to pay for imitator. This would be useful for both marketing and artistic projects. But probably less for marketing because they will want to go with step 1.
3. Teach yourself to talk like X. People who need to learn to talk like a particular person / have a particular accent could learn quicker. Just think - you will be able to supplement your comedy routine with kickass Christopher Walken impersonations any day now!
Variations of 3 and 2 together open up interesting modes of aesthetic impression, but I won't go into that here. But definitely I have some ideas that might benefit from being able to do this.
Surely software that communicates with people using natural language should be topping all these lists. Direct communication through voice with a local LLM is already possible. It won't be long before it's fast enough to approach natural interaction (if we can solve the "when is it my turn to speak" challenge) and then we enter a new phase of digital interaction and AI training.
A legitimate use, in the abstract, is one where a particular individual is willing to have their voice used to say X. The entertainment industry - movies and games - are likely to want this.
But if it's trivial to use somebody's voice to say any arbitrary thing, then it'll be done. Combined with deepfake videos, the result will be the ability to show anyone saying anything, including lies and things they find incredibly objectionable, in a disturbingly realistic way, and more so as time wears on.
The fundamental issue is that we don't live in a rights-respecting world. Making it easy to utter anything in the voice of anyone will lead to many more abuses than legitimate instances.
People will get immune to it if they aren't already. It's already common to fake screenshots of tweets/etc. Not a real problem unless you want to beleive falsehoods, then you will anayway.
