[Question] what does a preamp do and it can be replaced by other gain or eq pedals?

Hello, ive been using a mustanf lt25 as my amp for a year and started to look into things like the hx stomp. Many setups have a fx loop between the preamp and poweramp, but the hx stomp also seems to have a preamp block. I understand that if i use this i can skip the preamp and only use the power amp, but im confused on what the preamp actually does. Is the preamp even necessary – Can i replace it with the drive and eq pedals? If not, what does it do on top of those things?