Well, the game is really more about 'wants' than 'needs' isn't it? An owner might have 17m of unspent payroll but WANTS to sign the stud SP and SS that can hit. He knew before setting his budget, but that was all the payroll space he could free up. Anti-cash guy would say "Tough, you only get $185m, deal with it". Pro-cash guy would say "If he wants to give up something to get more cap room, fine".
As far as needs, I'm not sure when you actually would ever NEED cash. Unless, of course, you screwed up budgeting or spending....but then aren't we right back to the standard cash in trades argument?