Steel vessels are strong, sturdy, tough and reliable. It's the material of choice for many offshore sailors past and present for the impact resistance the material possess, hence why high latitude research vessels are constructed of steel, to punch into, and not be crushed by, the ice floe. At the other end of the marine industry on calmer waters, canal boats can be produced quickly, effectively and, until very recently, cheaply using steel plates thanks to the simple shoe box shape of the traditional vessels, which is simply reinforced with steel angle and I-beams. With some practical and theoretical welding skills, a welder (or two) and some steel, any steel hull can be modified and refashioned again and again. This makes it a practical choice for a practical owner who is a dab hand with a welding rod, although you might struggle to move the steel on your own.
The shortcoming of steel is its tendency to corrode. It is not a particularly noble metal, and most other metals found aboard tend to be more cathodic, therefore it often suffers from galvanic corrosion. Modern epoxy coating systems, correctly applied to a steel hull are so effective that they can almost completely abate corrosion. Almost, because epoxy is still slightly permeable, however, 4-6 coats of epoxy inboard and out should offer the skipper a good ten years of corrosion free boating (as long as breached coatings are recovered, and anodes are applied when necessary!)
The inadvertent trend towards tech dependence in the boating industry is leading to electrically complicated vessels, and this is a detriment to many steel boats. Once upon a time a vessel had navigation lights, cabin lights, a VHF radio and a depth sounder. These days the average 30' GRP coastal cruiser might have a fridge, an autopilot, an electric windlass, electric water pumps, solar panels, wind generators, battery chargers and twin chart plotters, not to mention multiple plug sockets to keep myriad electrical items humming. Add to this the enthusiasm each successive owner might have with adding something here, like a TV, and ripping out something there, like an electric pump near the bilge, and before you know it, the vessel is an electrician's nightmare and stray currents from poorly installed and poorly grounded wires is almost inevitable. This charged stray current then 'leaks out' into the surrounding water by way of a bare wire in contact with bilge water for example, which then conducts the keel bolts or stern gear and is transferred outboard.
The problem is exemplified in marinas if the power source is not properly installed and maintained, with hundreds of boats directly plugged into that bad source. It's so bad in some marinas that the colloquialism 'live marina' is often heard amongst the boating fraternities, with stories of anodes being consumed within weeks of replacement. The issue for the owner of a steel boat is that it is their boat that becomes the marina's anode once the sacrificial anodes have been consumed. This is why its doubly important to have a steel hull surveyed, inside and out, regularly.