When to delete old logs

Some of our system logs have been growing/accumulating since we went live in January of 2016. Last month when the system was down, I renamed the ladb, lase, and latm logs, and allowed the system to regenerate them when it restarted. What is a good standard/practice to have in terms of keeping/archiving the old logs? Are they not needed ... do I just delete them ... do I keep them for a while (how long) ... ? If the answer is keep, or keep for a while, what value, or potential use is there for any of these files?