I was taught to heat the wire and touch the solder to it.
This looks like they are laying the wire on the solder, then heating the solder - not the wire. Won't this result in a cold solder on the wire?
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The OP uses single stranded wire but the solder blob on the PCB creates far more surface area contact for heat transfer from the iron which makes a large difference with stranded wire. When you're soldering hundreds of connections, the time savings from not having to pin the wire against a solid surface or clip it in place is substantial.
The bigger problem is that all the rosin flux in the solder will have evaporated, likely making the joint very weak. Most DIY projects lack any form of strain relief so it's a double whammy for any wire that will shift around.
>"The bigger problem is that all the rosin flux in the solder will have evaporated"
But the OP specifically adds short pieces of solder to the pads before soldering wires. When they finally lay the wire and start heating that solder piece might have just enough flux in it. Alternatively one could just smear some flux on the pad before laying wire.
Still I am not convinced this particular way is of any practical advantage.
Flux helps break the surface tension between solder blob and wire so I really doubt the flux in the unmelted solder would have a path to flow to the wire.
But yeah, my solution is to just dip the wire in a jar of flux as I’m stripping and twisting them
Not just the wire...the entire joint needs to be heated equally (ideally) and then the solder is touched to the heated joint. Any time you touch the solder to the iron it will burn off the flux and cause cold joints.
Never put solder on the iron tip...although...I do it sometimes to increase heat transfer to larger joints (emulates a larger tip) but you can expect that the flux has burned off and may require liquid flux and reflow.
Sidenote: if you coat your tips with solder before shutting off your iron it will prevent oxidation and increase tip life.
Yes, this will result in a cold join that will be unreliable.
Lots of the joints in the images are sub-standard. This method is fine if you're happy bodging something together, but it's not great.