:eek: And what does balance have to do with it? It will affect something else, the game itself ;) Don't lump everything together again. Isn't balance and diversity the same thing? No. Ruining a weak upgrade really won't affect the balance much.
In particular, the meaning is clear: your price balance is disrupted, which will make housing conversion an automatic action (without a choice). The same thing threatens your warehouses and mines if you leave cheap warehouses that give significant discounts, motivating the mass construction of warehouses and mines.
If you think that automatic housing conversion and the widespread development of warehouses and mines is good (i.e., a change in gameplay, not the addition of new, balanced features), that's a different question.
Added 6 minutes later
Unfortunately, the developers made too few upgrades that are really worth using at different points.