Fun story: I pushed back on the implementation of an A/B testing platform and instead said we should focus on improving performance and my Marketing VP literally walked out of the meeting in anger. Infrastructure work is never sexy, but it's so important to everything — even sales performance.
A/B testing small changes is something that really big sites like Amazon can do because they have enough volume to justify it. It's kind of like blood doping in sports. If you're already at the top of your game it will make enough of a difference to be significant, but if you're just some average person who can't run a mile... blood doping is the last thing you should do.
Just yesterday I was watching a video about a triathlon bike which uses a frame setup that's illegal in normal bike racing. The question was, was it a faster bike? The conclusion was that the bike was quite heavy and not very stiff, so not really a great bike for normal bike racing. However, as a time trial bike where drafting is not allowed (the normal situation in triathlons), this bike could shave off 40 seconds over 40km. Which is a pretty huge amount, the presenter said with a grin.
He said it with a grin because it is a huge amount in the context of a competitive time trial -- like the difference between first place and 10th or 20th place perhaps. But as a percentage difference it's roughly a 1.4% increase in speed (assuming you can maintain 50 km/h). It's practically nothing in real terms.
In competitive cycling, though, the margins are super small. You might win the Tour de France by 2 minutes, which seems like a pretty big lead, until you realise that's 2 minutes in 80 or 90 hours of cycling. This is why Team Sky's approach of "marginal gains" is so successful -- the difference between first and second place is something like 0.04% performance.
We've got this idea that we need to optimise performance (in terms of SEO, etc, etc), but I've never seen anybody quantify the margin of "victory" required. How much better do you need to get to push you over the edge? Because that's what's going to dictate what strategy you need to pursue.
A/B testing small changes is something that really big sites like Amazon can do because they have enough volume to justify it. It's kind of like blood doping in sports. If you're already at the top of your game it will make enough of a difference to be significant, but if you're just some average person who can't run a mile... blood doping is the last thing you should do.