Against ACUs
Against slow units (Bricks, Percies and somewhat Othuums due to their shit pathfinding)
Against Sniperbots
when there's a stalemate, you force UEF and Cybran to either attack or retreat cuz otherwise they eat free dmg.
For a situation, let's assume you're Seraphim. Your t3 tanks are rather slow, but they have a strong short range cannon. So you want the opponent to go into your range. You form like an ellipse with your tanks and your sniperbots shoot at the opponent. Due to that (if he's not able to kill your sniperbots with enough own sniperbots, arty etc. which will most likely be the case due to your insanely strong mobile shields), your opponent either runs away (you gain ground) or he pushes into your othums (what you want cuz short range cannon).
For another situation see the tourney game Wreck vs. Blast on Emerald Crater.
You can keep them under a shield if you use selection deprioritizer and assist the sniperbot with a shield. So that's that aspect.
What they WERE and are NOT for anymore is "Oh I reached T3 stage? Time to build 5 sniperbots and directly push into the enemy base with them" which is no longer possible due to the need of a T3 PG.