you won't encounter any issues with datatypes until you try using a component like "add values" which calls specifically for a number/integer, and then if you tried to reference your "comments" variable, you wouldn't see it because the data types don't match (textbox = string/text, addvalues = number/integer). a good way to keep tabs on your datatypes is to right-click on any component in your workflow and choose "browse data", then click the checkbox at the bottom to show data types. depending on the component you right-clicked on, you'll see any variables being passed from upstream of the component you chose.
from the sound of it, the component you were trying to use may be modular and doesn't implicitly produce output.