Maybe you were raised sending thank you cards after every birthday party or holiday gift, or maybe you're just discovering the power of a well-timed thank you. There are many reasons to send an appreciative card to let someone know you are thankful for something they did or said. Here are a few of those reasons:

Thank-yous are like a receipt
If someone sends you a gift they don't necessarily know you received it unless you send a thank you card. When you send something it is reassuring to know not only that the recipient got the package but that they actually liked it. Thank you's are basically a receipt, but with heartfelt emotion showing you appreciate something. 

They show you're responsible
After a job interview send the person who interviewed you a quick thank you. This is a great opportunity to remind them that you would really like the job and that you are skilled and capable. Be sure to use proper spelling and grammar to show your full potential. Very few people send hand-written cards these days so you're sure to stand out for sending your interviewer a thank you.

Paper cards are more personal than emails
People rarely get personal mail these days. Hand-written letters are few and far between. Receiving mail is a sort of treat. Make the person you'd like to thank feel extra-appreciated with a personalized card.

They highlight what you're thankful for
Sure you could buy a thank you card and simply sign the inside. That's not very memorable. Instead, address the person by name and then say thanks. Use descriptive adjectives when mentioning what you are thankful for, such as the "thoughtful gift card" or "colorful photo frame." Tell the person how you will use what they gave you, such as, "I plan to take my wife out to dinner with the generous gift certificate you sent for Christmas," or "The money you gave us will be really helpful for renovating the kitchen." This way the giver knows that their present is being put to good use and will think that they were a small part in whatever you did with their gift.

It's better late than never
While a typical thank you card turn around period should be within a week you can always send a card later if you forget for some reason. Even if you are quite late after receiving the thoughtful gesture or gift it is OK to still send a card to let the giver know you are thankful. They will appreciate your thanks, even if it is a little late.