What's the benefit of pitching the entire starter?
My last brew I cold crashed the starter and poured 90% of the liquid off the top of the yeast cake then let the cake come up to wort temp and pitched. Then you don't have to worry about any (very very little) drop in OG right?
The best answer in a short reply is "that's why you should read the book 'Yeast' by Chris White and Jamil Zainasheff." But I need to and will look again at my copy. edit: without having looked at the book, let me give a brief reply based on my understanding (which is somewhat limited, but well-practiced):
Because yeast is an organism you need to "ranch" it to have the best possible outcomes. In sufficient quantity and recent cell reproduction, and due to the ability to create a large population thru the "full ferment and decant" approach to yeast starters, you will be successful. But also, when yeast are at the height of their reproductive activity (FK starter) and again in sufficient numbers they will immediately go to chewing on the sugars of the wort, resulting in a fast initial reproduction/growth cycle that will shorten lag time and thereby ensure a good start to the large task of working through a high gravity wort without leading to poor health, population or mutations at critical phases of the ferment. I see it as insurance through a short lag time. Both approaches work. For me, doing a next-day impulse brew using old yeast (all available the day before brew day) in limited supply, a larger than normal full krauesen starter was the best option. And it worked, with minimal negative side. It's chugging very well in the ferment chamber I am happy to report.