CFI here. It’s not a big deal in most of the country but the Pacific Northwest does have variation of about 20 degrees. It can make a difference when calculating takeoff and landing data as winds are true but runways are magnetic.
The adage goes “If you read it, it’s true. If you heard it, it’s magnetic.”
[1] https://www.faa.gov/documentLibrary/media/Order/7900_5D.pdf Chapter 7.4
airplane inbound to land: "KXYZ tower, N12345 at 3000' tower: "N12345, KXYZ tower, confirm you have Romeo" airplane: "KXYZ tower, N12345 has Romeo" tower: "N12345, fine, but bravo is current, recommend you recheck atis"