Guerilla tactics work on bigger maps with small teams. If you spec, you will see a lot of matches where one or both sides porc at the front and do not attack or just have artillery standoffs. Had they used scouting to probe for weak spots, it would be possible for them to get into enemy economy with raiders, potentially dealing lots of damage. It's also fairly common to see cloaks used for trapping scenarios. You can bait enemies into crawling bombs (snitch, imp, skuttle). Cloaked reavers/knight and cloaked dominatrix are another thing that you might see sometimes. Scythe can get into the enemy backline sometimes, to snipe high value targets. Athena can fly in stealth and build units in the back of the enemy base, potentially even place a djinn to teleport units into the enemy base (some people use this to instead build porc in the corner of an enemy base, which only really wastes metal). Spiders and jump units can get to places other units can't, which can be exploited for surprise attacks. If you think you can predict enemy movements, you could stun them with a silo missile (or lure them into one) and finish them off with raiders.
Lobsters are another noteworthy unit, because they allow you to engage/disengage and generally get around very rapidly, and over cliffs.
And you of course have the classic gunship transports dropping units into enemy base (jacks, reavers) and newton ramps to launch jump units and bombs across the map.
If you can scout and exploit a weakness, it's always worth it, because it should be very cost efficient. Not to mention the metal the enemy will then likely spend fortifying and rebuilding their base after such attacks.
On maps with a lot of players the frontline is typically continous, there's very little room to maneuver without getting hit by stray shots or running into one of multiple counters to sneaky tactics (flea screens, badgers, firewalkers, outlaw boxes, walls of porc).
The other issue is that anything not stealthed will almost certainly be spotted by radar, I don't know that many maps where radar is blocked by terrain well enough to allow sneak attacks. Raiders are good units, but they scale the worst of all units in the game, due to having low hp, so in high numbers they just end up blocking each other from having line of sight to shoot while dying in droves, including to death explosions of big units and buildings, which often cuts short successful raids, micro is definitely very important for this. If a game gets to that stage, you might be better off using some of the faster/more durable assaults (ravager, hermit, knight, jacks), depending on your goals.
