Leaving gaps between your natural teeth can affect your speech and your ability to eat and chew properly. Gaps between teeth can also make your smile look less attractive, which can affect your self confidence. In some cases it can also affect the other teeth as they start to shift positions over time.
Replacing any missing teeth improves your smile, can make you look younger and more attractive and can also improve the variety of food you can eat. This can lead to an overall improvement in your health as you are able to have a more balanced diet.