A trine can show an easy relationship between the planets involved, but as a result there can be a tendency to slip into bad habits which then go unchallenged. The good side of Saturn trine Pluto is an ability to see where existing structures need to be transformed - a capacity to dig deep in confronting one's self-limiting beliefs. But this trine could also dig deep to protect one's existing reality, resulting in controlling tendencies which the native is less likely to question (and life is less likely to challenge) than would be the case with a challenging aspect.
But it would depend on the chart as a whole - personal planets aspecting both Saturn and Pluto, orb of the aspect, how strong the planets are by rulership, and the general attittude of the chart to the kind of determination and heaviness shared by Saturn and Pluto.