One of the most power-hungry components in a traditional laptop is its hard disk, and time between charges can be greatly improved by keeping the disk in sleep mode. On machines like the OLPC that have solid-state disks, keeping disk writes to a minimum improves the life of the drive, minimizing unwritable sectors. Depending on how your machine is configured, log activity from kernel events and running daemons like sshd, a dns cache, or a local copy of apache can force your disk to make tiny writes every few minutes, impacting flash drive lifetime and ensuring that a mechanical drive never sleeps.
One solution to the problem is to disable syslogd entirely. An alternative is Ramlog, which offers a bit of a compromise. With Ramlog installed, log data is stored in RAM until shutdown, when it’s copied back to disk in one big write. You will loose your logs if you have a system crash, but in a more usual scenario where you’re trying to track down a wireless problem or an apache error on your development laptop, the logs are there for you to examine.