3 Leaf vs 4 Leaf Antenna (tx/rx?)

I'm a little confused about 3 vs 4 Ieaf antennas. Is there any strict rule which one goes where (and why)? I can see that some sites are selling a pair (4leaf) saying they are compatible for both tx an rx. some other said putting 3 on tx and 4 leaf on your rx goggles is better. Is there any real advantage of mixing them?

Thank you in advance.