When Parker gets the ball he looks to give to someone, mainly Modric, immediately because he knows he hasn't got the skills to play a 45yard pass out wide or dribble round someone. This keeps the ball moving fast and importantly means it gets to a player who can create an opening sooner.
Sandro is a better passer, so when he gets the ball he will survey the options open to him. He can switch the ball from one flank to the other, but equally he can be caught in possession or slow our play down, with the opposition getting closer to the likes of Modric before he receives the ball. Comprendy?
I don't think i agree with this summation.
I would say that Parker is too limited to do anything other than play the quick short pass - which is not always a good thing, it hinders us some of the time too.
Sandro has more ability to run with the ball and open up spaces in the oppositions midfield and defence. He does very occasionally get caught in possession but it is usually in an advanced part of the pitch.
Both have their pros and cons as you say however i would say that Parker does limit our game due to the fact that as an opposition team you know that you don't need to have anyone marking or closing down Parker properly as he offers zero forward threat. So defensively he offers a lot, in an attacking sense (which a lot of our football is based around) he actually weakens the team far more than Sandro.
Furthermore whenever Parker slows us down by doing that bloody stupid 'spin in a circle' thing he doesn't have any ability to pick a more adventurous pass to make it worthwhile, and so it ends up going to Modric who's now got a man in his face.
With Sandro injured a lot and Livermore only really breaking through we needed him, but to be frank I think both of them have the potential to be better players than Parker and that Sandro is there or thereabouts already.
Provided he's still here next season he should be a regular starter - the question remains as to with whom and what formation. Believe Modders will go, so will he provide the cutting edge we need if played purely with Parker or Livermore - think not.
What last night showed is that when play with pace out wide it we benefit. So we need back-up for Lennon as he has been injured so much this season and Bale needs to remember the position that scares defences the most, and that we need cover in that position.