This question has dogged me, as I purchased my own home in 2010 but around 2012 began to stay more with my elderly folks for reasons regarding illness/need (mine and theirs). I always regarded my own home as my primary residence but now (for tax purposes) wonder about that.
“A legal residence, also known as a domicile, is the place you consider your permanent home. It's the state you intend to return to after a temporary absence.
A person's legal residence is important for legal purposes, such as: Determining jurisdiction or choice of law, Determining a person's tax status…”
I have heard that if a house is sitting empty and the insurance company discovers that, they will drop the coverage because it is a higher risk of fires, vandalism, etc. Should there be an issue, the insurance company will investigate and may not pay.
Years ago we had a neighbor that also owned a house next door where her daughter lived. Just to be sure, for the homestead exemption, she would sleep over on New Years Eve to justify she was there when the new year started for tax purposes. One house was in her husband's name.