The trends feature in sellerboard helps you keep track of all important KPI's for every product to make sure you don't have a negative trend. Such KPI's are for example BSR, sales, returns, profit. If one of these worsened lately, the seller should take action (e.g. decrease price, check the quality, run ads, etc).
You can select a KPI (e.g. return rate) and a time frame and see a table with all your products and their month by month performance (including the value of the KPI and the % change in comparison to the last month).
Sorting the table will immediately show you all your problematic SKU's (e.g. the ones where BSR dropped in the last month comparing to the previous month).