"First wash... Then dry... What if it was done right away?"

Here are the main advantages of a washer-dryer (2-in-1) compared to separate washers and dryers:

Space saving

The biggest advantage. Ideal for small apartments where there is no space for two separate appliances.

Convenience

All in one: No need to move laundry from the washer to the dryer.

Automatic cycles: Some models start the dryer immediately after washing.

Aesthetics and ease of connection

One appliance - fewer hoses, less electricity, easier connection.

Looks better in the interior.

Price (sometimes)

One appliance is often cheaper than buying two separate good quality machines.

Less maintenance/repairs

One unit - less chance of breakdown in general (although the risk that in case of breakdown everything is lost at once).

Energy efficiency (in newer models)

Some modern washer-dryers have a heat pump, which saves a lot of energy.

Although washer-dryers have their drawbacks (such as less drying efficiency or smaller drying loads), if space is limited or simplicity is required, this is a very worthy option.