Use View > Customize Toolbar and remove any extraneous toolbar buttons and spaces.
Also, you can enable the hidden preference, WindowToolbarStyleExpanded. This displays the window title at the top of the window instead of the newer method showing it to the left side (which does consume valuable space). New windows would show the change in the title position.
Here are the two options and the effect on the toolbar search field…
Are you referring to local or global smart groups?