Expressions can be written, using multilines and comments. But once, the dialog is validated, it's rendered in a single line widget, making it less readable (eg, "Label with", "quick field calculator" in attribute table...). You need to reopen the Expression dialog to see the whole formula.
Having the ability to extend the widget to show the whole expression could be handy.
PS2: I haven't (consciously) noticed it until now but hovering over the widget shows full expression. So I'm no longer sure it's worth the enlargement (except, maybe to ease expression edit?)
Expressions can be written, using multilines and comments. But once, the dialog is validated, it's rendered in a single line widget, making it less readable (eg, "Label with", "quick field calculator" in attribute table...). You need to reopen the Expression dialog to see the whole formula.
Having the ability to extend the widget to show the whole expression could be handy.
PS: some comments at https://github.com/qgis/QGIS/pull/3805