[brightball]

The biggest issue with both that and the single drum units another comment mentioned is that if there's more than one load you still have to be on stand by to put it in, so you're only saving time on the transfer of a single load.

For the single drum units, you lose the ability to wash 1 load while another is drying. The perk is that you can throw a load in when you leave for work and it will be done when you get back home. If you have more than one those, you're extending your total wash time from

wash * loads + (1 dry time)

to

(wash + dry time) * loads

[makomk]

Though, given how... interesting the reliability is on dryers and especially single-drum washer-dryers, it's probably best not to leave them on while you're out if you want your house to be there when you get back.

[nradov]

Yes my relatives had a house fire caused by an unattended clothes dryer, probably something to do with the exhaust (exact cause couldn't be determined). I wouldn't leave a dryer running when I'm not there.