Self-incrimination does not apply in civil cases. This is actually a pretty standard warning against spoilation of evidence in a potential civil case -- if a party doesn't convey such a warning, then, in the event of ensuing litigation, the court is likely to find that they did not trigger a duty to preserve evidence on the part of the defendant.
If a defendant is so warned and destroys evidence, then the trial court may impose sanctions such as an adverse inference instruction (essentially, instructions to the jury that any evidence not produced by a side should be inferred to be damaging to that side's case). So any lawyer who stayed awake during civil procedure is going to make sure that they keep that option alive in the event they decide to sue.
If a defendant is so warned and destroys evidence, then the trial court may impose sanctions such as an adverse inference instruction (essentially, instructions to the jury that any evidence not produced by a side should be inferred to be damaging to that side's case). So any lawyer who stayed awake during civil procedure is going to make sure that they keep that option alive in the event they decide to sue.