In-line-four engines like our 1.8Ts need the dampening of crankshaft vibration to prevent the breakup at high engine rpms. This is not singular; flat-plane V8s can disintegrate themselves as well if undamped. For this reason, modern straight-four engines use a damped metal-rubber crank pulley - or a Fluidampr pulley, for whomever is ready to take the cost.
Alternator pulley is also a one-way clutched pulley. This makes it heavy, nearly 1 kg, compared to 0.13 kgs for an aluminum pulley. Lightweight pulleys on alternators do not bring great benefits, since most effort taken by the alternator is to overcome the magnetic eddy currents during electricity generation.
Power steering pump pulley may bring some gain if they are also underdriven - release some small amount of engine hp otherwise needed to run the pump, at the expense of increased steering effort.
BTW: original spring-driven belt tensioner can take one underdriven pulley, either power steering or alternator, but not both, one needs shorter belt for it.