There are two huge advantages to SHDL...
1- It covers the entire area by which a grounded character can move. No matter what, one will hit if you stay on the ground, and if you jump, the other one will hit you. This way you can keep them away or force them into a shield.
2- There is zero landing lag, so if you pull out a surprise laser up close, they're stunned for a short amount of time and you have a lot of options to begin beating the sh*t out of them.
SHL does reason two effectively, but not as great for one.
Spamming lasers on the ground is a decent option for the very beginning of the match (i.e. first 5 seconds) to surprise the opponent, but that's really about it. The time it takes for Falco to put away his gun is just silly. Grounded lasers don't cover any of the advantages of SHDL. The only advantage it has is that a laser may hit the opponent and keep him away, and SHDL, of course, can do that.
Just wondering... Why do you ask this? Are you having trouble SHDLing?