Balance: a fundamental principle of design and life.
Balance is a concept that we all understand intuitively. If an object is unbalanced we feel unsettled in our gut. The Leaning Tower of Pisa is interesting primarily because it is unbalanced. Without the tilt is it just another beautiful freestanding Italian bell tower. The questions asked about it all center around how imminent is its fall and why it is tipped. (And yes it is in danger of falling and has been since it was first built on marshy ground. It is about 17 degrees from vertical.)
Balance is a term of many uses. If a person is unbalanced, we generally react with alarm or concern at the evidence of mental instability. If a newspaper article is unbalanced, we assume the writer has a prejudice or has an axe to grind. It is very easy to be put off by lack of balance. If a scale is unbalanced, we know we can’t trust its findings. If a checkbook doesn’t balance it is because your record of expenditures doesn’t tally with the bank’s. In all these cases, our first reaction is to correct the imbalance.
The same is true if the design of a slide in a presentation is out of balance. Balance, where the right and left sides have equal weight, is a mostly subliminal indication to an audience that they are in caring hands. Are the titles or the full-screen images properly centered? Does the text on the left properly counterbalance the image on the right? Using an overlaid grid is a great help to establishing a balanced slide. Pay attention to how the two center lines, vertical and horizontal, slice through the screen. Now you have four quarters and each should be in balance with each other.
Checking my presentation for balance is one of the last things I do because it is easy to nudge something out of line while checking spelling or removing a line of text.
Of course a designer can purposefully create a slide that is out of balance or asymmetrical to make a point. But that’s an entirely different story.