Cashtab maintains state by periodically refreshing the utxo set at a fixed interval (10s). When the app detects a change to the utxo set, the user interface is locked until all utxos have been "hydrated."
In this context, "hydrated" means "processed by the server to determine if the utxo is an eCash or eToken utxo and, if an eToken, what token information does it encode?"
Sending and receiving transactions change the utxo set in ways that can be calculated. With better utxo management, it's possible to only "hydrate" the individually changed utxos (instead of the entire set).
Implementing this successfully can drastically improve the speed of the app.
Some work has been put into this in D9570. However, the implementation is not trivial.