What I have noticed so far with green wood is longer burn time overnight, nice bed of coals. Green wood isn't that bad to burn IF you have a large bed of hot coals and a raging fire in the burn box. This means more checking and more filling throughout the day which is hard thing to manage. The big issue is when you wake up or have unexpected demand on the wood overnight or you can't make it home and you have smaller coals. Throwing green wood on these smaller coals will pretty much just drop your boiler temp extremely low and in many cases snuff out fire and be left in a situation where you have to nurse the boiler for hours trying to get temps back up. Burning green wood can be done but is going to cause you headaches and much more time monitoring the furnace, plus burning more wood in the long run.
I will add, if you have a nice fire and bed of coals and throw some large green wood on top.. I'm assured a longer burn time, but wasting BTU to boil off the water on the added green wood. My lesson so far been to stock up on well seasoned wood, but also having a stash of green wood might not be all bad for long overnight burns in the coldest months.