It depends on the logs, why you're monitoring them and what type of information is stored in them. Most of the time, mail logs that just record who sent what e-mail to someone will not hold much value. However, if you have SSH recording unsuccessful login attempts, it could have some great value to you.
If this is for one of your systems, can you provide some detail on the services that are running on it, and what information it logs?
As for location, can you clarify? Most logs are stored in /var/logs, if that is what you were wanting to know.