You can use two kinds of Trends,
Internal, is an estimate of how well our Product will perform in time.
Market, is an estimate of how well the whole market including Stakeholders expectations and competing products will perform in time.
The purpose of Trend is to give us a better comparison (Benchmark) for the degree of improvement or change we are Planning or achieving, than we would get by using the more static Benchmark “Past.” Trend makes us plan to cope with the future, not just the Past. It makes Systems-Engineers think about the competition.