The frozen pipes are a 2 part concern.

1. Some homes use hydronic baseboards (aka hotwater baseboards) and have high amounts of insulation. If they set a low temperature the heat may not cycle often. Their baseboards are on exterior walls and may pass through unheated cavities. These can freeze quickly with -30f temps.

2. If your house has regular plumbing it may be in areas that freeze quickly, like the pipes under the kitchen sink. You can open the cupboard to fix this issue, but often there are pipes in closets or wall cavities that share space with vents that exit the roof. These get really cold too.

Having a higher ambient temperature will prevent a lot of issues in these areas.

I don't think the propane would freeze unless you're trying to use a small propane tank for the application. Like a grill tank for your fireplace could be an issue this weekend when it isn't in seasonal temps.