When you rent, you are normally limited on what you can do to improve your home. You have to get permission to make certain types of improvements. Nor does it make sense to spend thousand of dollars painting, putting in carpet, tile or window coverings when the main person who benefits is the landlord and not you.
Since your landlord wants to keep his expenses to a minimum, he or she will probably not be spending much to improve the place, either.
When you own a home, however, you can do pretty much whatever you want. You get the benefits of any improvements you make, plus you get to live in an environment you have created, not some faceless landlord.