Lots of factors on a chain that contribute to it cutting well, or it not cutting at all, along with when to keep it and when to toss it, or replace damaged drive links, cutters or tie straps, some are worth repairing, others not so much.
chain new from the factory is a compromise to sort of cut in all different situations, and you can dial in your chain to the particular wood your cutting.
setup for hard dead wood is different to a green, or soft pine etc.
The amount of hook on the top tooth, ie how high or low you place the file on the tooth, high placement of the file gives less hook, lower placement of the file gives more hook.
less hook is more durable and smoother, but slower, more hook can be faster, but the end of the tooth can be less durable, and more grabby if taken too far.
The angle the top tooth is filed to, 25/30/ 35 deg, or 10 for milling, more angle again makes the end of the tooth less durable, especially on chisel chain.
how much you take off the raker, too little and the chain will not self feed, and create dust and cause wear on the bar due to it being dogged in and leaned on to make it cut. Too much, and the chain becomes grabby and bogs the power head down. If its like that, forget trying to plunge cut, or cut smaller bits of branch.
The rakers are just there to determine how much of a bite the cutting tooth takes, and if you have different length cutters, but the rakers are all set correctly to each individual tooth, the chain should still cut straight and well, (providing the bar is in servicable condition), its not as efficient as each cutter being the same length, but it works, and enables you to get more life out of your chain instead of taking cutters back to the shortest damaged one, and loosing half of the life of the chain in one sharpening.
On hardwood, its better to run rakers higher than soft wood, as you wont overload the power head as the cutting tooth takes less of a bite into the hard wood.
on soft wood, the power head can easily drag the cutter thru the soft fibers, and you can take a bigger bite of soft wood, thus the lower raker height setting.
when a chain tooth gets worn, the height of the tooth lessens compared to its original height, along with its width, or the kerf it creates, and you can in some instances use a smaller file as has been mentioned.
Say your on semi chisel with a 5.5mm file, you could go down to 5.2, and even down to 4.8, as the 5.5 file ends up cutting into the tie straps, and leaves less hook all in one pass.
Basically what your trying to achieve is to maintain the amount of hook the tooth started out with, or what you want for your particular situation.
Ok, been trying to write this whilst being thrashed by my family playing amoung us. hehe.
hope it makes sence.