Quote from nitro:
Because they are human and often cannot keep up with supply/demand coming into his post, he often freezes the book while he matches buys and sells, mostly market orders with size (usually > than what can be accomidated by NX as a limit order.) nitro
That is one of the major reasons why the specialist needs to go.
For example, take yesterdays WHR/MYG announcement. The specialists gapped and held orders for MINUTES before making prints that were POINTS above the last trades before the news broke.
WTF kind of "efficient market" is that? Gapping stocks for points without any trades going off is hardly efficient.
In an electronic market, a trader has an opportunity to get shares instead of waiting for a random block print 2-3 points higher.
Again, that is just my opinion.
