Very often when we tell children to do something, their standard reply is, “But can’t I do it later? I want to watch this match on TV!” — or something like that. They always try to put things off, and they provide all kinds of excuses as to why things should be postponed. They will keep arguing with you till they are blue in the face. When you tell someone that you don’t want any `ifs and buts’, what you mean is that you want them to stop arguing and do what they have been told to. It’s your way of telling them to get on with their job. You don’t want to hear any more excuses.
Example: I don’t want to hear any ifs and buts. You are not wearing that dress to the party.