The left list with the not used commands is far to small. In the default width not all items are entire visible. The paired field with the command description is so small, that it nearly always needs the vertical scrollbar. Whereas 1/3 of the right list is unused white space. On my screen the default width is 8cm for the left list and 11cm for the right list. It will become worse, when the left lists gets icons too. The left list has always a horizontal scrollbar.
While the needed space depends on the theme and the width is sufficient here, it is always good to provide options to adjust the UI. Ideally we place a splitter between the left part of the UI from search to description. This control would be placed in the background of add/remove, which is quite uncommon. Alternatively, on resize both the left and right part resize equally. Muhammet, what is possible?
On my screen, only in the menus tab is the left column to small (this is caused by the long tree paths found in the menu category drop down list). I would assume the simplest thing would be to have both columns containing the function lists should have the same size.
Muhammet Kara committed a patch related to this issue. It has been pushed to "master": http://cgit.freedesktop.org/libreoffice/core/commit/?id=e970395c692a5c315914ddf5b43cf01e590345ff tdf#112241: Improve column width behaviour in Customize dialog It will be available in 6.0.0. The patch should be included in the daily builds available at http://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More information about daily builds can be found at: http://wiki.documentfoundation.org/Testing_Daily_Builds Affected users are encouraged to test the fix and report feedback.
Both lists are now equally sized (the left one got larger). And the dialog can also be resized by the user if needed.