TTLs are an integral part in of DNS - they can directly affect the amount of query volume that is attributable to your authoritative service, and in the event of needing to quickly change the record, can result in longer than expected change propagation to all users.
For records that leverage a sort of advanced traffic management scenario, such as NS1’s Filter Chain, it’s best to keep the TTL as short as possible. This way, when a change is enacted by the system, users on the other end requesting the name are given the most recent information. It’s worth noting that most recursive servers do not actually understand a TTL shorter than 30 seconds - while we won’t stop you from going lower than that, the results may not be favorable in the long run.
For records that rarely change, such as TXT or MX records, it’s best to keep those somewhere between an hour (3600s) and a day (86400s). When it does come time to enact changes with regard to these types of records, it may behoove you to change the TTL down to a shorter interval before enacting any changes to ensure that the changes are propagated quickly.
For help with random label traffic (which logs against your base domain), you can edit the NX TTL value to a higher value, causing resolvers to not re-request that same domain again for longer. If your active domains do not have answers changed frequently either, it would also help to increase their TTL value as well.