...to make sure you still have it.
I had a client contact me recently to let me know the contact form on his website wasn't working.
The problem turned out to be his web host had updated their servers with new software and the script that powered his form wasn't compatible with the upgrade.
It was quick to resolve once we figured out the problem. Still, it served to remind me that things change with hosts from time to time and that it's worth checking out key website features to make sure they're working properly.
This would be especially true for sales forms!