It depends on what Nature you have. Each nature has different effect.
Almost all natures increase a stat by 10% and decrease another by 10%. Although, there are some natures that don't do anything at all. Natures like Docile and Serious do not do anything. Those "neutral" natures are usually the bad ones - no one uses them. I believe there are 5 natures that are neutral.
For example, a Brave nature increases the Attack stat and decreases Speed. That means a Brave Garchomp's Attack stat will be 10% higher than a Serious Garchomp's Attack, only if they have the same IVs and EVs.
A good natured and IVed Pokemon is hard to come by. A perfect "flawless" IVed Pokemon is a lot rarer than a Shiny or a PokeRus'd Pokemon. Now getting a good IVed and natured Pokemon is near impossible.
Usually Pokemon don't really need flawless IVs. A sweeper like Garchomp probably doesn't care about it's HP, Defense, or SDefense IVs because a sweeper doesn't really use those stats. All Garchomp cares about is it's Attack and Speed IVs. So as long as those are high, and you get a good nature (Jolly), you're fine.
Don't forget that natures NEVER increase the HP stat. Only IVs and EVs determine HP.