Wealth can be useful, and can convert better than disbanding units. Here is an example from an emperor game, after discovering economics. Cavalry cost 80 shields, and disbanding them generates 20, so the rate is 4 to 1. So 4 shields are being spent to make 1 somewhere else. But wealth converts at 4 shields to 1 gold also. How is this worse? It is only a worse conversion if you use the gold from wealth to hurry production, which is what I would assume you would be using the disbanding units for. In this case, hurrying costs 4 gold for every 1 shield (unless it is the first building turn, then its 8 to 1). To hurry with gold from wealth would actually be using 16 shields to get 1 somewhere else (4 shields to 1 gold and then 4 gold to 1 shield; 4x4).
Consider: say a city produces 24 shields a turn. It would take it 4 turns to produce an 80 shield cavalry, but it would actually make 96 shields, generating 16 shields of waste. On wealth that same city would make 6 gold per turn with a net of 24 gold, and no waste. Of course a city making 27 shields still makes 4 gold, so watch out for that. and blah blah blah, yadda yadda
before economics wealth probably should not be used. Unless you want to lose quickly.
After economics wealth can be important when you are in a democracy (or any other gov above its unit support limit) and need some tech, but don't make enough gold per turn to support units/maintenance etc. Setting a city that makes 60 shields a turn on wealth gives 15 gpt to help advance science.