Ok here's my input and i hope it may help.
Of course i'm always looking at the s&p and Nas futures and any major break should be looked out for.BUT i'm always looking for that something that is slightly different .
ie A sector that dosnt want to participate,a major index that suddenly diverges, a general that isnt trading like the overall market and in the Nasdaq watching MSFT and INTC like a hawk.Because if they falter the Nas 100 falters and that can cuase a divergence from the S$P and the Dow.
Many on this board will remember that it was the Nasdaq's divergence from the other two indices that started a major down trend in March.The island reversal which the Nasdaq made is in the market chat thread at that time.
If MSFT and INTC are so important to the Nasdaq then it makes sense to be able to view them and understand the way the are driven by watching them on their respective level 2 screens.Doing this puts you ahead of the game and not behind it.
Take yesterday for example. If MSFT has a $2 run in a day thats good.So if it reachs the whole number ie $52 how do the players feel about taking it through.You guessed it they didnt want to know.That was evident from the level 2 screen before it appeared on a chart .At the same time INTC is middle range bound and due for its normal flip flop.So if one was trading the q's this was a good indication that at that moment it was a good one to take profits on any longs.Looking at the other two major indices didnt matter.
It was also a good time to think about closing out any longs in other Nasdaq positions.I prefer to watch those two level 2 screens for my direction of the Nasdaq100.I want to see in advance how the big named mm are setting themselves up to play important support and resistance levels.When they've made up their mind i'll take my position and then no doubt when they transact at those levels their trades will be reflected in a chart price and the rest of the market players without level 2 Nasdaq will then be able to see the outcome slightly behind,pause whilst their favourite oscillator confirms the move, pay a spread,take their trade in some antiquated way and guess what it'll be the level 2 scalpers and mm that will be selling to them.
Intraday trading involves having the best and i mean the best,market trading information and exucution software to put yourself ahead of the game not behind it! Otherwise you will be losing the edge and money on every single trade taken which will slowly eat into your account. Of course this is only a personal view.