Currently include() is an extension by Viacheslav. It does not work if a variable is defined in a for or if environment. According to him it is not possible to include this feature in the extension. That's why I add this request to include it as a smath core feature.
Include is very useful when performing larger calculations. You can do simplified sheets for the sales department or give different permissions to the different files. If a sheet contains more than ~4 pages it's easy to loose overview. Include is a go-around. That's why we need a universal include function!
This topic was also discussed in the forum.