I disagree...and I have visited hundreds of companies over 30 years. Unless you understand the businesses you visit and what they do, you'll get a 'dog and pony show', and that's all.
The old "call the company" routine is a red flag, and I have lost count of the people who have visited now defunct companies and given glowing reports on what they have been shown.
Check the financials, look at the same ratios as banks look at. Check out the people running the company, and ask lots of questions. Check the answers to the questions for veracity, and never get sentimentally attached to a company or investment.