I think it's useful to have white lights on all home defense weapons, both handguns and long guns. I also have and use handheld lights. The handhelds are for searching for and IDing a potential threat when using a handgun, and as a backup to the weapon-mounted light during engagements; the light on the handgun is for engaging the threat, and if applicable, controlling the threat until police arrive (one hand for handgun and mounted light, other hand for phone). Lights on long guns fill all these roles.
My handhelds and weapon-mounted lights are Surefires. If your lights are for serious purposes, then don't buy cheap junk.
Re lasers: they can be useful in certain instances such as in low light engagements, engaging very fleeting targets, making engagements in circumstances where you can't bring the weapon's sights to eyeline, for shooters with compromised vision, as a training aid to identify poor trigger technique, etc. I don't use them as much as I once did, because I find they actually slow down my target engagement. I seem to take more time searching for the dot than finding the sights. I think that lasers increase rather than reduce the training load.