Table Menu Commands
While working in a table dialog box, the Table menu is often useful. Select some cells or rows you wish to operate on, and then choose a command from the menu (if no cells are selected, the command is applied to all the cells).
Table → Fill in Missing enters a probability into empty cells so that the probabilities of each selected row add up to 1.0 (i.e. 100%). Any row having no empty cells, more than one empty cell, or X cells will simply be ignored. The corresponding toolbar button is the one with the number entering the empty cell: 
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Table → Uniform Probabilities will set the selected rows of a probability table to uniform probability vectors, which means that all states of the node are equally probable. So all the cells of these rows will contain the number 1/(number of states), expressed as a percentage.
Table → Randomize works on probabilistic or deterministic tables. For deterministic tables it sets each selected cell to one picked randomly from the possible states of the node, following a uniform distribution (i.e. each state equally probable). For probabilistic tables it sets the cells of each selected row to randomly selected probabilities. Of course, the probabilities of each row will add to 1.0 (i.e. 100%). The distribution of the probabilities entered is not uniform (it favors numbers closer to 0 in an attempt to better match realistic distributions). The corresponding toolbar button has one die over the = 4 && typeof(BSPSPopupOnMouseOver) == 'function') BSPSPopupOnMouseOver(event);" class="BSSCPopup" onclick="BSSCPopup('X_PU_relation_symbol.htm');return false;">relation symbol: 
Table → Remove will convert all the selected cells to empty cells. If there are selected cells, then pressing the delete key will have the same effect. The toolbar button consists of the = 4 && typeof(BSPSPopupOnMouseOver) == 'function') BSPSPopupOnMouseOver(event);" class="BSSCPopup" onclick="BSSCPopup('X_PU_relation_symbol.htm');return false;">relation symbol covered by a red X: 
Table → Build From Other Net will build the cpts of your current net based on the cpts of another net. More info
Many of these commands can also be done from the net window, without using any table dialog box, by selecting the nodes of interest, and then choosing the menu command from the Table menu. It will apply to the entire table of all the selected nodes.