Will The True Tweakers Please Stand UP

I'v Been Hearing So Much About Tweaking(tweak for speed,tweak for power)It Would Be Realy Helpful If Someone One Could Explain The Defferance Between The Two(science) & The Reasons Why + How. I'm Trying To Build 45 Chiefs,I'm Serious About My Tribe.I Have Plenty Of Bases Waiting To Be Born,But I Want To Be The Daddy.