Horizontal mattress suturing is a fairly useful back-pocket trick to have in your repair arsenal. I don’t personally use these sutures often for primary repair, as they don’t create as meticulous of a wound edge apposition as simple interrupted sutures or vertical mattress sutures.
I find these sutures most useful for temporary placement amidst a difficult repair with high tension. Sometimes, it can be difficult to bring those wound edges together to facilitate simple interrupted suturing. The placement of a horizontal mattress suture can overcome this barrier, as shown in this video.