You can place text boxes on top of shapes but there are some disadvantages.
Alignment of text in shape is more difficult
Below is an example where we need to evenly distribute all the shapes horizontally on the slide.
In the first example the text is part of the shape.
So I select the first row of shapes and I click the Format tab, then Align and finally I choose Distribute horizontally making sure that Align to slide is active.
I repeat the procedure for the second row and press F4. So two operations to get a result.
Now the slide looks like this:
When I select the first and the second row separately and apply Distribute horizontally the slide looks like this:
Even if I select the shapes and the text boxes separately and align them, the result is not good. So it requires a lot more work to distribute the boxes horizontally across the slide.
Animation of shape and its text is more difficult
Let us consider the same example. I wish to animate the shapes of the first row by applying the Float down effect. The second row with the Float up effect. All shapes and the accompanying text should be animated separately with one click.
So selecting the first and second row is enough to apply the desired effect. There are only six animations needed to animate each shape.
See the following video:
If the text boxes are placed on top of the shape the animation is more complex. You need to select more, all shapes and text need to be animated individually. That takes 12 animations in total.
It is more difficult to keep the text in the shape.
If you add more text to the shape there is no problem when text is inside the shape. If the text is on top of the shape you need to realign.
Further more, if you adjust the size of the shape the text which is in the shape will realign automatically. If the text is above the shape it will bleed outside the shape. Grouping the shape and the text will not solve the problem.
Working in the Selection Pane is more difficult
The selection pane will contain more items so will be less clear.
Moving content on the slide, or to
other slides is more difficult
Moving shapes will take more time and effort.