Should I specify cell height in masonry grid?

Question

css

I want to use masonry for a grid of advertising banners

. I will set the width of the cells through percentages. there is an example in the docs

.grid-sizer,
.grid-item { width: 20%; }
/* 2 columns wide */
.grid-item--width2 { width: 40%; }

About the height. Do I understand correctly that it must be specified directly in the rule for the cell:

.grid-item {
  height: 295px;
}

.grid-item--height2 {
  height: 590px;
}

Or is it better to let the content inside the cell define its height? What is the best approach?
UPDATED: in the official example, the author writes the height directly in the rules for the cell. Does he do this purely because he has empty cells in the example (in a real example there will be content) or does he recommend this approach?