If you bookmark a comment/post it lets you hook a reminder to it. This should be especially helpful to those of us who need reminders to either send someone seeds, ask how a project is doing, or remember to ask for seeds, etc. To use it, simply click on the three dots on a comment or post, find the bookmark icon and click it. It will open a popup that lets you set a custom reminder. Very useful
Sidebar navigation column: Click on the three lines in the upper left corner to show or hide this feature.