Unless you have a drill press, drilling holes for homemade PCBs is a hassle. Not only the drill bit is quite fragile at 0.9mm in diameter, drilling holes off-center would also throw off alignment, making it difficult to insert and solder. Since I mostly work with SMD components, using through hole headers also create the headache of through-hole plating. Of course there are SMD male and female headers available for purchase but each SMD header pin is usually 10 to 100 times more expensive than normal through hole header pin, even at when bulk bought at the quantity of 1000.
This method is used everywhere since it's not new. It's just that people don't tend to think to use of these sort of solutions unless they're cornered.
Step 1: Place Down the First Blob of Solder
Put down a blob of solder onto the first pin you want to solder. Since I'm right handed, I prefer to hold the soldering iron with my right hand and hold the pin header with my left hand using a pair of tweezers. Thus I solder the right-hand side of the header first.
Step 2: Solder the First Pin
Heating the blob of solder with the iron into liquid form, align the desired pin of the header in it and make sure to align the rest of the header with the header footprint. After removing the soldering iron, keep holding the header in place to ensure the alignment is secured as the solder solidifies.
As you can see, the header does not have to be perfectly aligned on top. It doesn't even have to touch the PCB.
Step 3: Solder the Last Pin
The most outer pin on the opposite side is then soldered to hold the header in place before the rest of the header is soldered. This is being done instead of soldering the immediate pin because if the soldering iron tip is big enough, it may melt the previously soldered pin. The header may fall over and you would have to start over.
Step 4: Solder the Rest
After the header is securely soldered, the remaining pins are soldered.
Step 5: Final Product
There you have it! The ability to solder through-hole pin header without having to drill a single hole! The above photo shows a recent breakout board of mine having a total number of 22 header pins soldered with this method.