In B4J and B4i it is especially important to use the designer as the designer script and anchors are reapplied when the parent is resized. If you create the layout programmatically then you must also handle the various resize events and take care of resizing the layouts.
I use ABPlugin to add extra functionalities to my app. But as the plugin is compiled to libraries, I cannot load layout files, so I have to code the UI, which is a bit inconvenient. I have to deal with all kinds of anchors and size settings.
In B4a I like to add views by code which is good for me (first to learn how it works, now more "I'm used to it"). In B4J I only use the designer. Don't ask me, why B4x has developed enourous since I started so the designer is now a "pro tool" which I strongly recommend.