There's an old trick for transatlantic flights that you buy three, adjacent economy seats to enable you to stretch out and sleep. In theory (or perhaps in the old days) this was a useful tactic when you consider that that business class seats generally recline only 15% and when you consider the potential price differential (three $500 coach seats combined are often half the price of a transatlantic business-class fare). Smug travelers have boasted of the virtues of this travel tactic.
But what are the caveats? First is the potential armrest disappointment. As seat guru pinpoints, most commercial aircraft configurations include a row with armrests that don't lift. Rows 16 and 32 on a Continental 777-200, for instance, are immovable. As you may know, even rows that have lifting armrests only lift so far. You get a little bulge in your back. But obviously, there is a workaround to that problem to the armrest issue. Other concerns include that you have to fly with an airline that accepts multiple bookings from a single passenger (Continental, Delta and Virgin Atlantic accept multiple bookings as of this writing). Further, the small print in most airline booking rules includes a clause that they can never guarantee seat assignments. (Search Google for the phrase "guarantee seat assignments" and look at the wave of negative declamations you reveal.) After booking and payment your contiguous row of seats can be broken up by the gate attendant or by the mechanized caprice of a computer. And then there is the difficulty that many flights these days are booked to the gunwales with standby passengers waiting in an unruly line. You can be in a difficult position trying to defend your two empty seats when there is a line of passengers hungry to occupy them.