Interesting question. Just had a discussion on this in a chat room yesterday. Using T&S along with the bid\ask and price movement, I equate to "tape reading" which goes all the way back to stock speculators in bucket shops. To get good at it, you really need to watch it for months and months, day in and day out, and try to catch almost every tick. Obviously, the goal is to trade with the strong hands which equates to large lot size on the t&s.
Where the T&S for es helps the most is at the market turns at support and resistance. Yesterday morning is a good example. The weak hands were panicking, selling 1027 down to 1025, while the strong hand (read large lots) were buying.
In my discussion yesterday, the question was raised, "since you only see one side, (the buying the ask and selling the bid) you don't know about the large order on the other side.
My answer to this is the large orders are less concerned about the extra tick and are more likely to buy the ask or sell the bid. In addition, if you don't think that is true, you have to at least assume that the balance is the same on the bid and ask orders as it is on market order, i.e. large lot traders have an approximately equal amount of limit orders at various prices as compared to their market orders, so the indicator is still valid.
The next question was, "All trades are balanced, and require a buyer and seller, using t&s is like getting in the middle of a cat fight."
My answer is yes, all trades are balanced, but you want to see the t&s as an indicator of buying and selling pressure. It is just an indicator like any other, that must be confirmed by movement in prices. I am not interested in those times when the large orders are fairly balanced between buy and sell, like the proverbial cat fight. I am interested in the unbalanced situation where almost all the large orders are on one side. This isn't a cat fight, this is lions feeding - don't be their lunch.
Related to this, you used to see some tricks in the es bid\ask A year ago, you could fade the big bid\ask, because it was almost always a false order by a big trader, trying to get the little traders to front run it. When they had accumulated enough contracts, they would pull the offer and start buying, with the result that if you were trying to front run that big order, you just sold near the low of the day. This isn't happening so much now with volume and b\a size increasing in es, but you should be on the alert for it if you are a "tape reader." A year ago a b\a size of 1000 contracts would scare other traders. Now it take more like 4k or more, and with other large traders (firms) using es, they could get filled.
You may notice also after a while, that some large orders for "fake" support\resistance (a few ticks away from the present b\a) are entered and pulled by a computer program, because it occurs so quickly.
Good luck on your tape reading.