Furniture tends to leave marks on carpet where they sit dormant for months and even years. The good news is the marks can be removed in easy steps.
If you have marks on your carpet from where heavy furniture has been sitting for a while, place ice cubes on the area affected. Allow the ice cubes to melt into the carpet, and then completely dry. Afterwards, grab a vacuum cleaner and vacuum the carpet.
Your carpet should now be as good as new!
If this doesn’t work, repeat until you are happy with the effect.
NOTE: This probably shouldn’t be done with delicate carpets, and ideally you should test on a piece of carpet that is out of sight.