nyhuntfish,
When using multi-strand cable/wire rope, such as 7x7, 7x19 (1x19 and 1x7 are classified as single strand cable) the following apply. If you have a swaging tool, you put the sleeve(DF) in the correct size notch sideways, start at one end and keep swaging until you run out of sleeve. If you only have a hammer, lay the sleeve flat and pound it flatter.
A swaging tool has the correct size notches designated to specific sized sleeves (aluminum is different than steel) and when swaged sideways like demonstrated in that video clip, won't allow the aluminum to swage out the sides like you are doing when hammering any stop or sleeve, but restrains the sideways movement of the aluminum to the dimension of the notch, in the swaging tools jaws. The reason to start at one end when using a swaging tool, is that the sleeve or stop, elongates with each compression, and adds additional length to the stop or sleeve, which allows more number of compressions per fitting/sleeve/stop.
What you are doing when you swage or pound a stop/sleeve onto any wire rope, is swaging the aluminum/steel/copper/bi-metal into the voids of the cable/wire rope. The denser the material is in the stop/sleeve, the more amount of tonnage you need to move the material, to fill the voids in the cable. With a swaging tool, and the correct sized stop/sleeves, you are filling more of the voids in the cable from about 75% of surface area. When you are pounding a stop/sleeve you are just filling the top and bottom of the voids in the cable, and not getting as much compression of the material the stop/sleeve is made of. The denser the material swaged into the voids, the finished length of compression, and depth of compression all add to the strength/weakness of the finished product. Not all cable/wire rope/sleeves/stops, are created equal, manufactured to the same specs, nor quality of material. With a swaging tool, you can also swage a sleeve full length, turn it 90 degrees, and also swage the fins/ribs left by the first swaging process to gain additional strength.
What bctomcat has demonstrated above, is causing an interruption in the surface of the cable, or made the metal denser by applying a deeper compression of the sleeve in that direct area where pictured. There are commercial machines that swage in three stages that leave two large dents in one side of a sleeve and a single dent in the opposite side. Industry claims it exceeds cable strength.

I use my 3lb hammer but hit them flat just hard enough to squish them tight just a couple of taps.
J