If you decant the bulk of the starter wort first and to avoid pouring yeast down the drain then you need to either cold crash the starter so yeast go to sleep and settle out or let the yeast go to completion and then they floc out (this would take several days). Either way defeats the purpose of reducing the lag phase as yeast have to wake up again when pitched into your full batch.
This is another reason why I rarely decant, but I've done it both ways and they both work. As long as you have good cleaning and sanitizing practices, the lag time isn't a big deal. I (like many homebrewers) have waited until the next day to pitch lager yeast so the wort would be at the desired temperature and have made excellent beer.
The other reason I rarely decant, other than what I stated in my previous post, is it allows me to decide to brew less than 24 hours in advance. With my job it is often hard to plan a brew day enough in advance to chill a starter for decanting. It's just easier for me.