Over time, the filter element will get clogged with debris. This will lead to higher pressure drop. The filter element has to be cleaned periodically to unclog the filter and prevent the filter from breakage.
The open area will affect how frequently the strainer must undergo maintenance. A strainer with a higher open area, such as a basket strainer, will need less frequent cleaning than a y-strainer.
Usually, the open area is compared to the pipe size. For example, the user may demand an open area that is 3X of the pipe size.