How bad is to ALTER tables from an upgrade point of view ?

[Farcaster]

It really depends on what you're trying to do. If you want to add a field to the user table, for instance, that will then be made available on posts and in the user arrays, then adding the column to the user table will prevent you from having to do manual edits to add table joins. If, on the other hand, the field will be accessed infrequently, you may want to consider adding a separate child table.