Major benefits to scanning the galaxy?

Question

While continuing my quest for Reaper annoyance dominance by pinging, I found that I can get cool stuff on planets by scanning!

Is there any major benefit for avoiding my main goal and taking the time to pick up this trash valuable resources or am I perfectly fine to go on my merry way of ping-doom?

More specifically, how much would it hinder my quest to avoid scanning anything at all? (outside anything required)

Would it severely cripple the War Assets or are they necessary boosts to help the player that wants to do SP only?

Answer 1

If you're going for single player only, you really should scan and collect War Assets. It's been made relatively clear that if you intend to avoid the multiplayer completely, you're going to have to be severely OCD about collecting items and running side missions to get the best ending.

Sometimes you can learn about a War Asset by overhearing or participating in a conversation on the Citadel or the Normandy, which will give you a clue as to where to scan for the item. Other times you'll find the asset first, and then have to search for the person who could utilize it.

If you plan on playing multiplayer extensively, you might be able to get by with less scanning of planets.

Do note that planetary scanning is much improved from the boring mineral scans in ME2, so don't be afraid of these activities! Finding a War Asset on a planet generally takes less than a minute or two.

Answer 2

If you don't scan at all and you don't gather any Readiness via Multiplayer, you're almost certianly going to come up short and fail to get the best ending. Scanning contributes 1850 war asset strength.

you need 5000 to get the best ending, so this is a very substantial chunk

Here's a Scanning Guide which will help you locate the most resources the fastest. Note that asset locations are predetermined so you can just seek them out right away, you don't have to blindly stumble around. No planet ever has more than one asset, either.