You are making a sole application if there is just one applicant (you).

You are making a joint application if both you and your spouse are applicants (ie applying together).

A joint application removes the need to serve documents on your spouse.

A joint application removes the need to attend court if there is a child of the marriage currently under 18. If you are making a sole application and there is a child of the marriage under 18 then you will need to attend the hearing (attendance by your spouse is optional - ie up to them).