Values from preexisting cells can be used in the creation of new cell formulas, hide and skip conditions, functions and events, etc. Simply enter the desired cell number (without quotes) in place of a value. This will bypass the need to reenter function information already built for the cell in question, but it also allows information to be updated in multiple places throughout the document.
Consider the scenario that there are two map number values being brought into cells:
C100's function is MAP(BR,101)
C200's function is MAP(BR,102)
When it comes time to create a cell (C300) that adds these functions together, it is possible to shorten the function considerably.
Rather than MAP(BR,101)+MAP(BR,102), the function would become C100+C200.
Also, if map number 102 changes to 202 in the future, an update to cell C200 would automatically carry through to C300, ensuring the value remains correct.