incase you don't realise how drums work.
when you press the pedal it pushes a specific amount of brake fluid down the brake lines. this pushes the pistons out of the drum cylinders, which inturn evenly pushes the linings out against the inner drum and stops it from turning.
since the fluid is a specific quantity, your linings need to be just shy of touching your inner drums.
if they are not, then the fluid will just be enough to move your linings to your drums surface or to partially push against the drum.
hence you have to double pump to get them to work. once is to bring the linings to the drum, the other pump is to make them push against the drum.
the point of the snail cams is to move the linings out so they are just shy of the drum. then the first push of the pedal pushes hard against the drum.
the fluid will always go to the path of least resistance. so if one lining is not near the surface of the drum on any side, then the whole braking system is compromised as all it will do it push that lining out to meet the drum.
same with pads and discs. if one piston is sticky and not next to the disc, then when you brake it will push the pad out first and not stop the vehicle properly.
(this is ignoring dual circuits for this example)
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