Usually? No. For every six squads you give Frag grenades, that's another 10 infantry you could have. The only benefit of Frag is if YOU are assaulting the enemy in cover. That should NEVER BE HAPPENING UNLESS YOU BUILD A SPECIFICALLY ASSAULT ORIENTED GUARD ARMY. If you plan to stand and shoot, use your guns to destroy the enemy infantry and vehicles at range, don't rely on grenades.
That being said, if you ARE planning on designing an assault oriented guard army that plans on assaulting enemy in cover, by all means, equip them with grenades.
I find it's cool to model the actual models with grenades, but not actually pay for them.