Actually grounding serves three important purposes:
1. Dissipate static electrical build-up caused by mechanical forces (wind blowing across dish).
2. Direct faults in connected electrical devices to ground
3. Deter lightning by preventing charge build-up which would create leaders
The NEC requires that BOTH the dish AND all coax lines be grounded, #10 copper or #8 aluminum from the dish and from the ground blocks to the ground.
The ground used MUST be HOUSEHOLD ELECTRICAL GROUND which means NO independent ground rods unless they are NEC compliant in nature and installation AND backstrapped per NEC to HOUSEHOLD ELECTRICAL GROUND. That is the crux of it.
Too many installers ground if at all to gas lines, oil tank pipes, garden hose spigots, etc. If a ground loop fault is created in your system, it can cause fire, electrocution, death.
Statistically, more lightning strikes are NOT to grounded dishes. The installer lied blatantly.
What DOES happen is that the ground can act as an antenna, receive a good EM pulse from a NEARBY lightning blast, and carry it back to the receiver. A surge suppressor rated for DBS is always a good idea.