Smoke rounds are also fun, especially if that tiny rack is your only long-range weapon, like on the aforementioned Grasshopper. You can use the smoke to cover your approach, reducing the amount of damage you take before getting into your own weapons range. If you're in range but facing multiple enemies, you can lay the smoke to shield you from some of them, leaving clear LOS to the target you want to shoot at.
Be careful about moving directly into your smoke, though. Do that often enough, and people will get the hint that the smoke is telegraphing your planned move for the next turn. Good way to start eating more than your daily recommended allowance of artillery.
If your opponent likes to use indirect LRM fire, dropping smoke in front of a spotter can be a good way to force him to move, vacating a perfectly good spot or degrading the to-hit numbers.
If you play with fire rules and your opponent likes to use conventional units, a mech-heavy force can use incendiary LRMs to flush non-mech units out of woods or buildings.