Does anyone know if it is alright to leave some residue water in the pipe in subzero winter?

To be safe, we always add non-toxic RV antifreeze and use compressed air to push it thru the pipe till we see it come out the faucets, toilets, etc.

Also add RV antifreeze to all drain traps, toilet tanks, and bowls. Make sure water heater is drained.  Dishwashers and washing machines can be an issue too.

It is almost impossible to get all water out of the pipes, especially where there are low spot in the pipe where water will collect.

Better safe than sorry.

Not Sure about residue water.  However, I had the same issue years ago and all the water was drained by contractor and drain lines and pumps that need water was displaced with  pink non-toxic propylene glycol antifreeze.

Also, you can leave faucets slow dripping so water can run in pipe.  Running water does not freeze.

No comment.

It’s a technical question has to be answer by a technical plumber.

From my experience it is safe
 to leave a residual amount of water in the pipe. The concern comes when the water left in large volume in a pipe freezes. The frozen water expands and breaks the pipe. Residual water should not do that.

typical the standard for winterizing a house you need to, shut off the water, drain the water and using a air compressor blow out the lines. then for toilets, p traps and drains add marine antifreeze

The problem you could have is where water sits in a elbow or low spot in the piping, I have even seen toilets crack from water in the bowl or back tank. If the house is going to sit unheated in an area of the country that gets well below freezing for an extended period of time it is best to winterize. If you do not hire someone and want to take your chances at least turn off the water at the main and open all the faucets, shower, etc. Then go to each toilet and buy a few gallons of RV antifreeze and flush the toilet after the water is off so it can't fill and then pour enough in the back of the tank to flush it. Also pour antifreeze in each sink trap and shower trap. If things don't hard freeze for a long period of time you might be safe.  

I would say that is a risky proposition. If the water didn't fill the pipe anywhere completely it might be OK but if there's any place where it fills it completely, such as a low corner, it's likely the pipe would crack at that location if it gets cold enough. It only takes one burst pipe to ruin your day! I've seen plumbers use a compressor to blow out the lines to make sure they are empty but depending on the layout of the system it can be tricky. I've also seen them add a valve at the bottom of a system to be able to drain it down reliably. 

To my knowledge that should not be a problem.

The big problem with frozen water in pipes is expansion, causing the pipe(s) to burst.  If you only have a small amount of water in a system you need to find the lowest points where water can gather and evacuate it so that this doesn't happen.  A "low point" drain is usually on any system, and you should be able to blow out the system using a compressor.  Once the system has been purged, small amounts of water (drops) are not an issue.

Generally it should be ok as you said. However it would also depend upon how long the sub zero temps last and how much residual water is left in the pipe. Just to be safe just keep the valve open to allow water flow as a drip and also put some rags around the pipe especially on the pipe outside the building. Hope this helps!