How Calculate GPU Cracking Time
By an amplifier I'm assuming they mean something like adding generated or static rules.

[simplification] When you run with only a wordlist, hashcat is limited by the speed at which it can ingest and attempt those words, if you tell it to iterate through mutations of each word before loading the next one then the GPU will be able to be better utilized.

An example of this would be either of the following: (-g generates random rules, -r loads rules from a file.)

hashcat64 -m0 "my hash" wordlist.txt -g 100000
hashcat64 -m0 "my hash" wordlist.txt -r myRuleFile.rule

Run those commands and see the difference in hashes per second