I've used Small Lasers on many an occasion, but the arms and legs are the worst place to put them. If you're in short range of the SLs, they're extremely efficient from a damage per ton or heat perspective, even more than the ML, but that's also the time where you would want to do physical attacks. Putting them in the limbs means using one or the other, and wasting the other opportunity. Putting the SL in the head of the HBK was a good move, and I've used it on many occasions instead of a ML when I don't want to build the extra heat and slow my 'Mech down the next turn, but can spare a single point for the SL.
Ideally, one LL or PPC and a heap of SLs makes for a great backstab design or independent raider unit. The big gun punches holes, and then the SLs exploit those breaches. The alternative is MGs, which have their up side of generating no heat and slaughtering Infantry, but down sides of additional tonnage and risk due to ammo, and only 2/3 the raw damage against 'Mechs and vehicles.