By spelling and writing well EVERY TIME, you transmit the message that you are educated and that your opinions matter and should be taken more seriously. A person earns respect by communicating their thoughts correctly. I really can't take a spell check impaired person seriously when the message is conveyed so unseriously. I declare "unseriously" to be a valid word that should be added to the dictionary, if it's not already
Seriously, if you're in college and write home with errors in the letter, what is your mom going to think? What a waste of money sending that kid to college, perhaps? Or, they aren't teaching my kid much.