So, Thor pointed out to me that I was wrong in my assessment of deep striking Land Speeders. Obviously this makes some of what I said obsolete. Does getting a shot balance out getting cover? I'd say that it does, especially since the main reason you're deep striking is to get closer to the enemy in the first place. Since you can fire you can risk deep striking in Melta range although you're almost certain to be destroyed by return fire.
Down to the key point; when would I use it? On a board with not much cover the tactic definitely comes in handy. Usually, if you start with the Speeders on the board you should be able to advance them and keep them in cover. Also, if I was playing against a gunline army (IG for example) it would be a good way to get Multimeltas where they are needed without risking them to a lot of fire before they get to shoot. Obviously, as with all Deep Striking, you need to be careful with where you drop your Speeders but, as ever it's all about balancing risk/reward.