Bad Ideas - Laundry

Washing

Washing with no detergent

Causes grease & dirt deposits inside the machine. These gradually build up, leading to ineffective washes and bad smells.

Ecoballs

Same problem as above

Never using powder

Scum builds up faster when liquid without powder is used. Powder contains a mild scourer to clean the machine, and over time the lack of this much affects the cleaning of the clothes.

Never doing a hot wash

Occasional hot washes are needed to clean the machine itself.

Using washing up liquid as machine detergent

Soap residue creates scum in the machine. Scum attracts dirt and causes bad smells.

Never descaling

Scale prevents dirt removal, and on some machines gradually blocks the water level sensor tube. Scale is the prime cause of washing machine floods in these machines. Descaling in hard water areas helps to maintain standard of cleaning.

Low spin speed machine

Very low spin speeds (eg 600rpm) leave lots of water in the clothes, causing long drying times. And if dried indoors, damp problems. And if tumble dried, unnecessary electricity costs.

Bleach

Standard chlorine bleach makes some plastics brittle, and should not be used in (most) WMs with plastic tubs. Oxygen based laundry bleach is much more suitable for both clothes and modern machines. If you wish to use chlorine based bleach, the user's manual usually makes it clear whether such bleach can be used safely in the machine.

Top loading vertical axis machines

These use several times as much water and electricity per kilo of clothes compared to modern horizontal axis front loading machines. If you need greater laundry capacity, 2 front loaders stacked give several advantages over one big top loader.

machine failure doesn't stop washing being done
at end of machine life there's no big rush for a replacement, and a good choice/deal can be picked.
repairs are also unhurried, hence often cost less
much lower water use
much lower electricity use
hence much lower run cost
2 front loaders take more clothes than many top loaders
loads divided aver 2 machines mean wash programs can be different & optimised better

Drying

Draping wet clothes around the house

Drying clothes indoors releases all their water content into the atmosphere. When windows are closed in winter, high indoor RH generally causes condensation, which often causes damp, mould and rot. The more washing is dried this way, and the lower the washing machine's spin speed, the worse the problem will be.

This isn't such an issue when windows are open or a dehumidifier is in use.