Each surgeon has her/his own preference. Personally I like to perform the diastasis repair in 2 layers, using a permanent suture for the deeper layer, and slowly absorbing suture for the second layer. In theory, even if absorbable sutures are used, the body is thought to scar in the repaired position before the sutures absorb. However, in patients who may stress the repair with early activity, or aggressive activity, or weight changes while the area is healing, I want to have one row of permanent sutures to prevent the repair from widening or the diastasis from recurring. There is not generally any long term side effect of permanent suture, though one potential risk of any suture is infection of the suture. Given there is typically something else that causes infection and gets trapped in the suture material, by doing the first layer repair in a "buried" suture technique, I leave very little of the suture exposed to the surface. Then by placing a second layer of sutures, the entire row of permanent sutures is "buried" from the surface of the repair, or isolated from exposure to the adjacent tissue. Aside from what type of suture is used, the technique of diastasis repair is also a consideration, as is the overall tummy tuck planning and technique, and peri-operative care and post-operative care, so this question should be just one of many considerations.