You don't need to clean out logs, as they don't take much space and you will need them for troubleshooting purposes. You're not helping your Mac by deleting such files.
Logs are not a requirement for troubleshooting at all. They can be a very handy tool to pinpoint a problem/cause but it can also be very confusing (too much information). That's why there are systems like syslogd and the maintenance scripts. They only keep logs up to a certain part. Keeping nearly everything is absolutely useless.
How much of the logs will be kept is something that the sysadmin usually decides. It seems that in this case someone wants to limit the amount of logs to safe some disk space. I don't think it will do much harm. Most problems are instant and repeatable anyway so it is very easy to recreate errors messages in the logs.
Saying that he is not helping his Mac by doing this shows a misunderstanding of what a logging system is supposed to do. One should be asking himself what he gains by limiting the logging. In this case it's probably lot's of effort for something that brings you little gain in reducing disk space and amount of writes to the ssd making it pointless. The only thing you'll benefit from this entire process is gaining knowledge of various systems in UNIX (OS X in particular). The way OS X is doing the logging and clean up of old logs is fine. The defaults are good enough for the average person.
Can't some people or companies use apps that can read the files on my Mac without actually logging into my Mac? Isn't there a boot CD that gives that ability to read hard drives without actually logging in?
Yes there are, many. They all require physical access to your machine. Usually in security this means that all hope is lost anyway because they have full access to the machine which is why some people don't bother using encryption like encrypted disk images (standard in OS X, TrueCrypt, etc.) or whole disk encryption (PGP, Filevault 2, etc.). If you use encryption then of course they can't just read data, that's the whole point of encrypting something
To prevent somebody from booting into some kind of cd to get to the data on your disk you need to do at least 3 things:
- set up a firmware password with a strong password to prevent them from booting into anything other than your OS X install (this causes problems with things like single user mode, target disk mode, etc. for these to work you need to temporarily disable the firmware password)
- set up Filevault 2 or PGP in order to encrypt the entire disk (data will be unreadable when not unlocked; you do this by logging in as a user that is allowed to unlock it)
- change the read/write/execute permissions on your homedir so only the owner is able to read/write/execute to prevent other users on that same system to be able to see/read/execute files in your homedir
If you really want to be secure you need to power off the machine instead of using the hibernate/standby/sleep modes. This will clear the RAM which will disable the possibility to capture the encryption password (when using whole disk encryption with something like Filevault 2) via something like DMA (through Thunderbolt for example).
Security means that you need to apply it to several levels. There simply is no such thing as applying only 1 measure to be safe. Think of security as a plan, a design. Deleting logs or certain information in those logs is completely useless in this case. The actual data (docs, pictures, etc.) is much more interesting. You can't commit fraud, identity theft, etc. with information from most log files but you can with things like a picture from someone's passport, creditcard, etc.
