A commitment ceremony can be conducted in place of a marriage ceremony. There are no legalities involved other than the requirement that there is a statement to the effect of “This is a commitment ceremony not a marriage ceremony.”
Perhaps a couple may be planning to marry overseas but due to the inability of family and friends attending they may choose to have a commitment ceremony prior to their departure. This ceremony can be extremely personal and wonderfully enjoyable having an overall feeling of a wedding without the mandatory legal wording of the vows or the declaration that they are husband and wife.
Prior to the advancement of same sex marriage, couples had no option than to have a Commitment ceremony ,to openly declare their love as a meaningful commitment for life. Now they are free to marry in the same legal manner as others.
Should a couple be unable to provide all the supporting documentation prior to the marriage date and plans are too advanced for cancellations, at venues etc. then a commitment ceremony can be performed with the marriage taking place at a later date.