I like suppression fire when you have surprise... everyone gets hit and has to soak. Sure, on average against armored opponents you might not do much damage, but when you're potentially hitting a dozen or more targets at once, someone is likely to roll poorly and get hurt. You could do the same thing with a grenade, but suppression fire is likely cheaper and without scatter you can be perfectly precise.
Also, since there's no worry about net hits taking the damage higher, suppression fire is great when you'd rather not kill someone. If gel rounds aren't available, a Slivergun on suppression fire into a surprised crowd of unarmored targets more-or-less instantly clears a path without risking fatalities. (Admittedly, I wouldn't let that fly as a GM, particularly since critical glitches on some of the soak tests are likely.)