Damage beams with penetration > 1 and explosive effect do too little damage. The explosion effect is only applied to the first hit block, not to blocks behind it. Because of this a setup with 1000 beam and 1000 explosive effect modules loses ~45% of its damage, since damage is halved for the entire beam, not only for the first damage instance. This makes this combination basically useless, except for very small groups, but those lack the damage to destroy blocks in the explosion radius.

At the top you can see the damage from 1000 beam/1000 exp. effect, the left window shows the corresponding info. The right window shows a setup with 1000 beam/0 effect. The actual damage numbers for directly hit blocks look as if the exp. effect wasn't present. The effect modules should double the overall DPS, but they only add ~5% (assuming the first block in line had 6 surrounding blocks).