People don't often, or if ever mention this, but when it comes to casting 9 footers the system is all about false casting and double hauling, and for that you need room. But not too many people are willing to say that the system is designed to progressively load the rod, which is really much heavier than the rated load. Like for example a 9 weight 9 footer is rated on the AFTMA charts at 240gns, but ideally you need to get a load of 360gns to fully load it.
You achieve that load by false casting the head to and from and double hauling which progressively loads the rod.
Depending on the number of casts and DH's, and of course the size and grunt available from the caster, the rod will end up with a load approaching, or about 2 weights up on the rating. Like for a 9 weight the real load is 11 weight, or 330gns.
Generally users of 9 foot fly rods don't know, or haven't been told that you can spey cast with the things, which intentionally or unintentionally restricts the use of such rods in some places.
The users of Spey/Scandi/Skagit or overhead double handed rods on the other hand realise that they have a very handy fishing tool in their hands because they get to know about the wide variety of applications available to them, and the lines available to them for their fishing. No matter where it is.
Over the years there have been developments of the Spey rods to include the other casting styles and today its a pretty technical sort of game.
Manufacturers now make special lines for every application, and the number of rods available are increasing day by day.
Mind you they aren't getting cheaper but they are getting better.
I'm not a very good example but I've moved into DH rods, overhead types, for salt water fly fishing and have ditched all my 9 footers, basically because they are not very energy efficient, casting is a bore and they are very short ranged. You can cast further with bigger flies with a DH rod than you ever could with a short rod. And thats regardless of opinion or brags.
One of the more serious advantages of DH rods is that they can, by a bit of jiggery pokery be used as spinning rods, or beach rods by fitting a couple of different, or rather a lot, of different type guides, like light bridge guides or single footers.
I have recently had a TFO
12x12 re runnered with singlefoots to make it a switcheroo rod, like DH fly/beach casting/spinning thing. I also had the butt of a 9 foot Shimano hefty spinning rod altered so that it can be used as a 9 foot double handed fly rod. Its heavy, rated load 30 to 60g, like 460gns to 925gns. While its difficult, like impossible for me, to cast one handed its easy to get a line going double handed.
Years ago I lived in Carnarvon in Western Australia and fished fly off some fabulous ocean rocks, mind you it was with glass fly rods then, but now Im planning to get fishing off those same rocks with DH rods, and hope to hook into some of the same meanies that blasted me to bits all those years ago.
Welcome to the real world of fly fishing. And I mean the REAL world.