While I can see their usefulness, Im hesitant to classify them as "needed" or "important." Im willing to bet that many individuals have successfully defended their homes prior to lasers being "en vogue."
Can they be an advantage? Certainly. But, are they necessary? I believe not.
It is entirely possible that one could become far too dependent upon a laser device vs. spending the necessary time becoming proficient with iron sights alone. Also, depending upon which laser device you use, you could either A: accidentally (or even purposefully) engage such a device when it may be inappropriate to do so or B: not be able to engage it at all (while under extreme stress) when needed.
Now, the crimson trace grips are a nice idea as they are easily engaged. But, I would think that this "usefulness" could contribute to unwarranted/accidental activation if one is not careful. Other devices, such as those activated by a switch (picatinny mounted lights), may be hard to activate during a highly stressful HD encounter (sounds impossible...but, you would probably be amazed at how such an encounter could render mountains out of molehills).
Also, if one trains with a laser on a regular basis, he/she may be more inclined to not consider their weapon "ready" until the laser has been activated...thus, eating up precious seconds during a violent HD encounter or again, run the risk of keeping the laser device "hot" when it may not be prudent to do so.
Again, I like the idea of a laser...I have one myself. But, after further consideration, I have personally chosen to go without. The laser device I save for training purposes only.
If I were to mount my laser device, I would consider it a "last resort" method at best, when it comes to HD. But, to be honest, I do sometimes struggle with whether or not to permanently implement a laser device...same goes for a weapon mounted light. For now though, its a gun, tritium sights and a handheld flashlight.
Of course, there is always the consideration of what a jury may/may not think about such a device.