I appreciate the sentiment here, but I disagree with the premise in the first paragraph. It sounds like the age-old "nothing to hide" argument.

I trust my SO with my location information and I have nothing to hide, but I don't provide it because they don't need it. That's it. Why should I compromise my privacy and potentially security just because I trust someone? That's dumb. They don't need it so I don't provide it, that's my primary reason and that should be enough.

I have other reasons too, such as:

• I don't trust my or my SO's phone manufacturer to keep that data confidential, and I don't want them selling that to someone
• I don't trust my government to steal that information en masse, and I'd really rather not trigger some alarm somewhere
• I don't trust most of the apps on my phone with location information, and I'd really rather not trust my phone's app security to prevent them from getting it
• breaches happen, and I'd really rather my location information not end up in criminals' hands

And so on. There's no upside and tons of potential downsides, so why do it?