The form no longer matches the property
A homeowners policy is written for an owner-occupied residence. Once tenants move in, the occupancy stated on the policy is wrong, and a carrier can decline a claim on that basis. This is the single most common serious error among people who became landlords by accident rather than by plan.
What you are insuring changes shape
You no longer need contents cover for a house full of your belongings, and you do need loss of rent, which a homeowners policy does not contain. The conversion is not an administrative formality; it is a different product with different parts.
There is a window where both are wrong
During the move, with your things partly out and no tenant yet, the property is neither owner-occupied nor tenanted and may be approaching a vacancy condition. That gap is worth managing deliberately rather than crossing quietly.