Here is a massive understatement. Customers are important.
Outlined below is 15 reasons (excuses if you like) to visit them:
Introduce new Team Members
New or revised Product Offerings
New Sales Promotions
Introduce another Product /Relationship into the business
Get an Update on their Business
Discuss Like interests
How to help them generate more Revenue
Discuss work complete and get feedback
Innovative ideas / discussions to build benefits
Hand deliver gifts etc.
Introduce new customers to them
Seminars & Events
To discuss their concerns about dealing with you
Special Events / Invitations
So, now you are out of excuses, time to get out of the office!