For example, you ask an off-the-shelf LLM to analyze your ECG data. The LLM uses a tool to call out to your ECG ts analysis library. The library iterates over the data and finds stats & ECG events. It returns something like "Average heart rate: 60bpm, AFib detected at <time>, etc...". The LLM has all the info it needs to give an accurate analysis at a fraction of computational cost.
On top of that, this requires a large annotated dataset and a pre-trained model. And correct me if I'm wrong, but I don't think it's possible to have a "general" model that could handle arbitrary time series data. I.e. a model that is trained on ECG data would not be compatible with stock market data. And there isn't a way to have a model that understands both stock market data and ECG data.