Just wrote a piece on Efficiency which includes good deal of inventory turnover.
Also let me put another line which may help in your understanding:
When sale is made product is moved from INVENTORY (BS) to Cost of goods sold in PL
Change in inventory is a resultant number, it cant be either positive or negative forever. For a long period if inventory is decreasing that would mean either company has a huge pile up or producing more than required. You have to read in conjunction with a. inventory b. purchase c. stores and spares d. in progress inventories.
Now if you carry a lot of inventory you would land up incurring high storage and carrying costs. In addition to funds that have been used to acquire those inventories. If funds are on debt like a working capital loan it will eat up your margin and ultimately PL.
But do not ignore pricing power before concluding. If inventory price is going up not bad to have additional inventory.Ultimately cost fluctuations will be more beneficial than carrying costs.
There can be many more inferences, let me know a specific case; we can ponder over.