the impact site is the first playable area in pikmin 1... its where you encounter reds and learn the main mechanics
theres like 2 parts here and a ton of pellets
you can grow something like 300 pikmin in a day after you get the engine
the second part can only be collected once you get blues. its in a pearly clam clamp :]
usually they drop a pearl that makes like. i dunno 50 pikmin?? or so ive heard. perchance
theres also like a ton of pellets in the starting area
so uh. this is just a place to go if your out of a certain type of pikmin