If check your loadouts you see that Shepard has a weight limit - your power levels switch according to the amount of weight carried. However, there is no such thing on squad members.
Do they also have a weight limit? If not, can you just fill all the slots with weapons?
Is there any use to putting the less weight mod on squad member weapons?
In the same way that they don't run out of ammo, they are not affected by weight restrictions
See here
Weight Capacity
Each class has a different amount of weapons that it can hold at one time. If Shepard is encumbered then limitations will be imposed. For example, power cooldowns will be extended.Weight does not seem to affect the power cooldown times of squadmates.
