Somebody has read about lineup optimization.
I mean you want your best hitters to get the most at bats but you also want them to be in a position to succeed. Ideally one would have talented players you can throw them around all willy-nilly but that doesn't happen for every team. I mean I just called one of my FA signings a slow Bonafacio.
DISCLAIMER: I HAVEN'T READ THIS ARTICLE PRIOR TO THIS POST SO I AM READING ON THE FLY. I may miss something or say something contradictory.
This blog (unintentionally a Jays blog) shows that while 3rd sees 4.61 ABs a game which is logically 3rd most although it shows they also are most likely to come up when there are 2 outs (likely many from 2 up 2 down 1st innings) (37%). So you ask yourself if it's worth the tradeoff of giving your best hitter more at bats.The article also states that 4th "has the most plate appearances with men on, the greatest percentage of plate appearances with men on, and the most runners on per game, on average". Makes sense to throw your best hitter there since it seems like the best time to succeed but they also have a decently high 2 out %.
I know some guys think putting your best hitter at 2 is the good too. I know the Reds had Votto there a bit last year and Bautista has hit there with the Jays at times. I think Bautista was due to injuries but it worked well for the time he was there. It seems like a good balance of giving him ABs while also not giving him bad out scenarios. The biggest thing you sacrifice is having him hit with men on base which for some may not be worth it. The two I mentioned also have a good combo of OBP and power so that could be what 2 (3rd best hitter in standard optimization lineup) is the guy who can get on base but hit for a decent amount of XBHs to knock in your high OBP guy hitting 1 or giving your 3 and 4( 2nd Best Hitter) better run expectancy percentages.
That BBB article is nice because it gives you all the data to play with and tweak to what you feel is a good idea.
Here is another article on it
http://www.beyondtheboxscore.com/2009/3/17/795946/optimizing-your-lineup-by