(Ha! I always say "but".)
There's a catch. Big projects are fine, and putting them out at the end of the year makes sense in many settings. The risk is in trying to put out too many too quickly. Any big project comes with risk. When you do many of them at once, you compound your risk, and make it harder to figure out what broke when you're troubleshooting.
If at all possible, give your big projects some breathing room. Push them out and then go work on something small for a brief period. It doesn't have to be long - a few hours or so - but it'll make life a lot easier. Use the breathing period to:
- get a new baseline of system behavior and identify behaviors and patterns caused by your large change
- reflect on what you've done and tie up any loose ends
- review the next big change in light of the new system behavior, configuration, etc.; does anything need to change?
Breathing room is good for humans and good for systems. Take it, if you can.