Sometimes you want to be able to attach a comment or document a decision that one made about a specific data point without having to create a separate variable to hold comments on a specific cell. It should be possible to give each data point its own unique property (a documentation note) that one can integrate at any stage in the analysis process. You already have this ability in terms of being able to identify a unique data point in and between different graphs so why not have a documentation property associated with each data point?
Also, it might also be interesting to attach a "history" component to each data value as well so that when a variable is the result of a series of different operations (a series of different equation steps) one can see how the current value of that data point was derived.
Just some thoughts as documenting decisions at the point that they are made can be essential in understanding one's data when you come back to it sometime later