It sets a hard outer horizon for the household. Children's schooling, a spouse's employment and any longer-term intentions should be planned against that limit from the start.
Plan the household against the outer limit
A five-year maximum is long enough to feel permanent and short enough to arrive without warning, and families who treat it as a distant problem tend to face it during a school year. The spouse's employment authorization comes with L-2 status and ends when that status ends, so a career built during the placement has a defined runway.
Children may generally study under the published guidance, and a child who turns twenty-one during the period stops fitting the dependent classification and needs their own basis to remain. Deciding early whether the intention is a defined project followed by a return, or a longer stay that would require a different route entirely, prevents the limit from making the decision by default.