My car is old enough to just have onstar which is physically disconnected. My phone I avoid adding personal data to (outside of messaging), I limit my browsing, and I've done what little I'm allowed to in terms of locking it down and removing unwanted features. Ultimately though, it's a necessary evil I'm still hoping to find a solution for.
> But I gotta ask. How are they using your personal data against you?
the answer is that they'll use your data against you in any way that they can if it works to their advantage in any way.
Companies don't care about you and your needs, they care about themselves and making money. The reason there is a multi-billion dollar industry around the collecting, buying, and selling of even the most mundane aspects of your life is that companies have seen that all that data can be leveraged against you to give them money and power and one way or another that usually comes at your expense.
Often they use the data they collect to manipulate you. Maybe they want to get to you buy something you wouldn't otherwise, maybe they want to shape your political opinions. Maybe they just sell your data out to others directly or they use that data to make it easier for others to exploit you.
It doesn't matter if it's Facebook selling your data to Cambridge Analytica so that they can try to swing an election, a group of activists who buy up lists of people who have visited abortion clinics so they can harass them, or a company or data broker letting people buy lists of individuals with low IQs and poor education, or lists of people who are likely to suffer from dementia so they can be targeted with scams, it's all using the data you barely noticed you were handing over.
Even when it's not intentional algorithms are constantly searching for ways to exploit you in the moment you're at your weakest. They can detect when someone who is bi-polar is entering a manic phase and push airline tickets to them since people in that state tend to make last minute travel plans. They can detect when you're tired, heartbroken, or under a lot of stress and anxiety and target you aggressively at those times using one trick after another to find whatever works best (both using what has worked for others like you and tailoring their methods to you individually), and they do it all without ever being explicitly programed to. The algorithms just maximize for results, and the ends justify the means while giving corporations plausible deniability for even the most egregiously exploitative means their algorithms employ.
In the US, companies like Google, Microsoft, Facebook, your ISP and cell phone company routinely turn data over the state with both three letter agencies and local police departments sucking up all the data they can. It's a huge violation of our rights and a threat to our freedoms.
Even the most well-intentioned company collecting your personal data is likely not doing enough to secure that data, and whatever data they hold onto is just waiting to be abused when a less scrupulous person takes over, or to be handed over when the company is bought or absorbed into another, or to be sold should the company ever go bankrupt or become desperate enough for the money.
One way or another, the data you hand over will be used against you, and worse you'll have no idea when it happens. Today people are turned down for jobs and denied rental contracts because of the data collected on them. They are charged more for the same products they buy online than what other people are paying. They are told a company's polices are one thing, while other customers are told they are something else. Their insurance premiums are being raised based on this data. Companies have even been shown to use this data for things as trivial as leaving some people on hold longer than others, but nobody is ever told the reason why those things happen. You have most likely already paid more than someone else, had your time wasted, been denied something, been mislead, or been rejected based on the personal data you've handed over.
Nobody is using your data to protect you or put more money in your pocket. It is always used to serve someone else regardless of what that does to you.