You would never work in the field or in the lab without having a clear procedure outlined first - nor would you ever skip tracking what you were doing. A systematic literature review is no different.
It is only only crucial that you keep track of what search terms you used, which databases you searched with what combinations of terms, etc. - but you also need to keep track of your search results right from the start.
This is where RefWorks comes in as your new BFF.