There is a difference between steam generator irons and steam irons. A steam generator iron actually has two major components. There is the iron itself, and there is a water container and steam generator apparatus. The two parts are connected by tubing to pass the steam from the generator to the iron.

The more common steam iron, as you know, generates its steam from water in a reservoir in the iron itself.

So, being that a steam generator iron has two components versus the one -- just the iron -- for a more common steam iron, what are the advantage of steam generator irons over regular steam irons to offset the additional complexity and expense of a steam generator iron?

Basically, they do a much better job, offer more flexibility and control, and reduce chances of damaging fabrics.

For occasional ironing, where professional quality results are not necessary or necessarily wanted, these ironing systems may be overkill.  But many fastidious users want those results anyway, so they will buy and use a steam generator iron system.  There are even some male users who find that they can do a much better job with a steam generating ironing system than does a typical shirt laundry service.

The primary market for these are homemakers with a heavy ironing load, for those doing specialty sewing and craft work, for tailors and seamstresses.  Manufacturers claim it is possible to cut ironing time in half and get much better results than with regular steam irons.  Often, both sides of a garment can be ironed at the same time.  Creases in heavy fabrics can be made with having to exert heavy pressure on the fabric. 

Because most steam generator irons can also be used vertically, they can be used as garment steamers.  Items such as drapes, gowns, and suits can be steamed.  Steam should be available at any angle that the iron is held.

Being that the water is contained in the separate tank, the iron itself is lighter.  The tanks hold much more water than stand-alone steam irons, so that allows an hour or two or ironing without requiring refills.  Naturally, the maximum time possible depends on the make and model, and whether light steam or heavy steam is being used.

Many brands can use just plain tap water. However, if the water is “softened”, a mixture of half tap and half distilled can be used, or just bottled spring water can be used..

Depending on the make, the tank can sit on the ironing board itself, or on the floor. If put on the ironing board, it should sit on a thick towel or heat-resistant pad, as some tanks get very hot on the bottom.

A steam generator iron produces much more steam than a regular iron, which makes it take much less time for ironing. Because more steam is generated and the steam is more powerful, less arm pressure is required, making the ironing process less tiring and time-consuming.

High-end iron steamer models have low-water indicators. Look for thermostats to control separately the iron itself and the boiler. That will allow the iron temperature to be lowered for delicate fabrics, preventing melting or scorching them, without losing steam. Another feature to look for is a switch to shut off the steam altogether, so it can be used as a regular dry iron. Look for a switch to lock for continuous steam or just to press for only when you want steam.

A steam generator iron should allow you to select moist (humid) steam for ironing cotton and wool, and dry steam on silk and delicate fabrics. BTW, these systems will not damage delicate fabrics by spitting out droplets of water, because the steam is generated in the tank, not the iron.

As mentioned above, these are probably too much for the casual, occasional ironer. On the other hand, for those wanting ironing results equal to or surpassing those of most laundries and dry cleaners, these systems can be ideal. They are more bulky, because of the steam generator, so storage takes more room. Also, the electrical power requirements are greater than for the more common irons. If you run them at the same time as a microwave oven, on the same circuit, tripping the circuit breaker is quite likely to happen.

The product reviews for steam generator irons are mixed.  Users universally love them, as long as they work.  That is, with some manufacturers and models, there are reliability problems, usually with switches and hoses, either from the generator to the iron or internal.  Since most (if not all) are imported, service and parts can sometimes be difficult to obtain, and expensive when found.  Look on Amazon, for example, for product reviews for the particular models you are interested in, to see what others have said about those particular models and customer service..  Look for a one-year unconditional warranty against defects.

BTW, when you search on Google or StartPage.com for these irons, use the keywords “steam generator iron” or “steam generator irons” (without the quote marks) instead of just “steam iron” or “steam irons”.  That way, you won't have to wade through a bunch of search results for conventional steam irons to find the steam generator iron search results you are looking for.