The primary factor to consider when splitting pairs is whether or not your casino of choice allows doubling after splitting (DAS). If DAS is allowed, you must have the proper basic strategy memorized. I see players make a lot of errors in splitting pairs, primarily with a hand of 8, 8. Most know that a pair of 8s should be split against all up cards, but most stand when they hold them against a dealer's 10. The cost of that mistake isn't huge, simply because a hand of 8,8 is fairly rare. But by standing, a player has an expectation of -.537% and by splitting (if DAS is allowed), an expectation of -.483% is realized. So, the extra money which is put to risk does -- in the long run -- give a better return. Think of it this way. Would you rather stand with a 16 against a 10 or hit an 8 against a 10? By splitting, you get to hit an 8. Incidentally, the numbers also indicate that splitting is best when DAS isn't allowed, though there isn't as big a difference.
As the true count goes up, you'll split more and as it goes down, you'll split less. One play which is justified by a high count is the splitting of 10s. For example, there may come a time when it's worthwhile to split a pair of face cards against a 6. I counsel my students to avoid that play since it draws such a negative reaction from other players at the table. I don't really care what the others at a table think of my play, but if the floor personnel are alerted to what I've done, their initial suspicion may be that I'm a counter. If they've seen me playing good basic strategy and suddenly I have a big bet out and I do something like splitting 10s against a 6, they're going to think I'm either very stupid or very smart. I guess it all relates to the image your projecting in the casino; if it's one of a 'wild man', then go for it. But if you're quiet, polite and a non-drinker, I'd advise against making the play.
All other splitting situations should be followed to the letter; especially that of splitting 4s against a 5 or 6 (if DAS is allowed). Most people don't have the pairs part of basic strategy memorized perfectly, so they won't know what's right or wrong when you do it and most think it's wrong to split 4s. Nothing quite like making the right play and looking like a dummy when you do it!
As you go through the numbers on splitting pairs, you'll see that some don't agree with those published by Stanford Wong and other authors. As I've explained before, some have been modified as a result of Friedman's study on risk-averse play, and I feel they take no advantage from you yet do lower your risk somewhat.