Agreed on all the responses thus far. The ability to distinguish values ranging from thousands to tens of thousands to millions, etc., is substantially harder if numbers are left-justified.
> 3. right-justified numbers come from precedents like excel or other > spreadsheet type tools and muddles the distinction between editable and > un-editable tables (at least data output in from query results is > un-editable, I know right clicking on a table in the browser to "view ... > data/rows" outputs an editable table)
When we first released pgAdmin 4 we forgot to right-justify numbers. Users complained. Lots. They need to stay right justified.
Right justifying makes it substantially easier to understand magnitude and makes it easier to get decimal alignment.