tickrate is the amount of times the server updates within 1 second, so on a 64 tick server your enemys position will be controlled and changed exactly 64 times in a second. on 128 tick servers your enemy position will be controlled and changed exactly 128 times per second. of course the position will not be changed if your enemy is not moving but i figured you'd understand that.
in theory you could see a difference between 64 tick and 128 tick because your enemy and you should move twice as smooth on 128 as on 64. on real time, no you most likely won't actually see it. i do not know if this is proven or not but i cannot SEE a difference. i can FEEL it tho. your movement should be twice as smooth as i stated earlier and i have the experience that i feel like i feel a difference, i did a test of 15 games with my friends on lan hosted servers and guessed 13 times correct, 2 times to high.