I'm the same, I use some cheap ESP8266 devices which have a temperature/humidity sensor attached. They submit their measurements every minute to a central MQ installation:

https://steve.fi/Hardware/d1-temperature-humidity/

While I don't have any particular reason for collecting the data it can be fun to look at. For example you can easily spot when somebody has a shower because the humidity spikes in the bathroom:

https://twitter.com/Stolen_Souls/status/848444075296641025

Naively I expected to track the weather, because I figure on a hot day the temperature of my living-room/etc would spike. Turns out this house is pretty well insulated so the internal temperature has essentially no relationship to the external one. I guess that makes sense in a country where you might have -25'C in the winters.

Nothing in particular. I just wanted a way to view the temperature and humidity in my apartment when I'm out. Also I wanted to know what affects the humidity in my apartment and by how much (for example, you can see when I take my morning shower). In the future I may use the data to control a humidifier to turn it on whenever the humidity drops below a certain level.