Advise on Excel-One file vs multiple Files to use.

I’m stuck with a small doubt and wanted to check what others usually do. I have dashboard picking data from 3 types of data (A, B, C), each of records, and I’m not sure how to store it — whether to keep everything in one single file or split it into 3 separate files (one per category). What I’m trying to understand is which option works better when data is this large in terms of storage space, speed (especially when I only need one category), and overall system load. I checked with two different tools and got opposite answers — one said keep everything in one file, another said split it — so now I’m not sure what makes more sense in real usage. In my case, I mostly work on one category at a time and usually from a local or shared drive. What would you suggest — one file or multiple files, and why? Also, any recommendation on format like Excel, CSV, or something else would really help.