I really am not sure.
Its either what @sneakernet said.
Or possibly its to put the data on the chain as smart contract like when you create a nft.
Id assume the latter but thats pure assumption on my part, just makes more sense to my brain that way.
Ive nvr used offers so nvr researched it.
there are different informations around. I dont remember if it was incrementation steps of 5 or 50.
I have also heared that everything under 100 counts as 0 and hpool clients wont even accept any transaction under a fee of 1000.
That beeing said, I think I am a little further now. I created offer files with an assigned fee and the fee balance got locked away (simmilar to when you do a transaction, just it does not show an outstanding sum)
My best guess is that this fee is now attached to the offer to accelerate the offer beeing executed for my customer. Once the offer gets executed, the fee will be taken and the rest will be released back to my account. Huh. What a nice way to lock up balance -.-