At school, at work, at home… closing loose ends is critical. By only completing 90-95% of the project, you are leaving 5-10% incomplete for an extended period of time. This can become a burden and the longer you leave it unfinished, the more difficult it becomes to finish. This 5-10% can negatively impact new projects because some of your focus is on incomplete work that needs to be completed. In the past couple of years I have found it very important to work through my projects and tie up any loose ends before moving on.
As an example, you may be working on launching a new product line. You are working through estimating a P&L (profit & loss) statement for this new product and you find that the product will not generate the net profit you once you hoping for. If there are no alternative solutions to create more profit for your profit, then you can mark this complete and communicate out to the team that you do not recommend going forward. If you did not complete the P&L for the profit and had this task sitting around for a while, then you would find yourself carrying unfinished work. You need to make sure you are finishing everything associated with the project to call it complete or finished.
As another example, you may be working on cleaning your home. Lets say you vacuum/mop all your rooms except for 2. You say you are going to get back to them when you can. Most likely you are not going to get back to them for a long time and you will constantly keep thinking about them whenever you see them. In this scenario, just spend the extra time needed to finish the job and move on. It feels so much better to complete all the work instead of having to eventually go back and complete the job.
These are just a few thoughts I have about closing loose ends.