In the Lightning Network protocol, Hashed Time Locked Contracts (HTLCS) are used in the construction of channels. A new HTLC is required per route that the channel is serving in.
In BOLT #2, this maximum number of HTLCs in a channel is hard limited to 483 as the maximum safe size to prevent the transaction from being too large to be valid. Adding more HTLCs would interfere with being able to broadcast and confirm a transaction.
Therefore, similarly to how congestion control is handled for normal
transaction, lightning channel updates can be done across an OP_CHECKTEMPLATEVERIFY
tree, allowing nodes to safely use many more HTLCS.
This has the benefit that less data would be used to close any individual HTLC in addition to permitting more than 483, so it may be useful to use CTV even if there are fewere than 483 HTLCs.
Because each HTLC can have its own relative time lock in the tree, this also improves the latency senstivity of the lightning protocol on contested channel close.
errata: previously, this page suggested that the limit was 12 for LND, which was incorrect (12 was the field number in the struct).