1. Email is faster than snail mail. Unless you’re planning on driving back the next day, your letter isn’t going to get to the recipient fast enough to boost your chances of getting hired. And while some potential employers are impressed by the person who drives back the next day, some find it creepy and intrusive. Remember -- you're trying to impress the receptionist, not make her feel put-upon.
2. Thank you emails allow for supplementary materials and information. In your thankyou email, you should always offer to provide references or any other material that could help with the hiring process. And, if that’s something the hiring manager wants, he can simply respond affirmatively on the thread, instead of having to go out of his way to reach out to you to request it. And this is a two-way street -- if you have additional questions or want to check in about the hiring timeline at any point, an email will help facilitate that a lot more efficiently than a handwritten note.
3. Thank you emails make follow ups easier. Emails create a thread that will help the hiring manager (or person you've met for an informational interview) remember you down the line. Hopefully you’ve mentioned something specific and personal in your note, and the chain will jog the reader’s memory of you when it’s time for him to make a decision. It will also remind him of what has been previously discussed, so he can give youaccurate information moving forward.
As you can see, emailed thank you notes are a crucial part of the job application process. If handwritten thank you notes are your thing, that’s fine, just make sure you send them in conjunction with a thank you email.