Quick water heater bypass valve question

Yeah, drained everything, low points, water heater, fresh tank. Then added air psi with everything closed except WH drain. Then closed WH drain, and blew out everything one at a time. Toilet, shower, sinks, outside shower.

Never touched bypass valve.
So, IMO I see no reason to touch it. WH was pressurized with air, and was drained. In fact, after I had disconnected the air compressor, I still had air psi in the plumbing. I opened the bathroom sink for some reason and had air psi come out.

Im not trying to debate, I obviously don't want to bust any lines, but I just don't see how it needs to be bypassed when using air. If anybody can show me why, then I will gladly do it.

The reason why I don't want to bypass in the first place is because the WH is under the kitchen sink and needs a panel to come out to access it. Not a big deal, but I just don't see a need to do it.

BUT, I will be accessing it anyway now to check for vertical hose with water in it as Bumpy mentioned.

I am taking air compressor with me anyway, because I forgot to blow out the black tank flush.

Thanks guys!

Well, if you leave leave the water heater by-pass open, you'll need to pump a 6 gallon tank full of air ... enough to get it pressurized, enough to continue pumping that air through the rest of the system.

If you do not drain your water heater, you will only blow out some of the water heater water, most will remain in. Intake to the heater is at the bottom. You'll pump air through the water. Out-Take is at the top of the heater. Once the water gets below that spot, you'll be pumping air, but not water.

Drain the water heater, put it on by-pass, then pump the air! When done, flip the by-pass back on. If you pump the pink, leave the bypass closed until you've flushed all your lines in the Spring. After flushing the pink, THEN un-bypass the water heater so no "pink" will get in it. If blowing only, drain, bypass, blow, then un-bypass so it will fill automatically with water in the spring.

depending on configuration, there could be standing water in a vertical pipe beside the WH unless you turn that valve and let it drain.
bumpy

IF you are just blowing out and not pumping anti-freeze then no NEED to bypass water heater

Bypassing is so you don't have to use GALLONS of anti-freeze (fill water heater) to get anti-freeze into hot water system

Open water heater drain, open rv low point drains and then blow opening closing drains/faucets etc (water heater drain plug will need to be back in place to build pressure/blow hot lines)

Yes you do need to be in bypass before blowing out. Any water upstream of the WH will end up in it if not bypassed when you do the blowout.