If your TTL is very low, you end up creating/handling a lot more DNS traffic, because your records are flushed from the cache more often and have to be re-retrieved. Also, many public DNS servers (e.g. your ISP's, or Google's) set a minimum TTL on all records (overwriting any lower value) to minimize DNS traffic/requests. Setting your TTL to an hour is fairly standard, but some DNS hosts (especially old ones) will leave the defaults set to something like 48 hours for no real reason.