What is this part?
 

I found a huge crack in this part (see photo), I am not sure what part this is but the crack is about 6-7" long running down and around the back side of it. Is this a necessary part to have? or can I just remove it? I had a mechanic at my local Les Schwab look at it and he said to just remove it and it will be fine (of course I didn't ask him what it was called though I know I should have just didn't think of asking) but I wanted to get some 2nd opinions before I go taking a part out.

it looks like a vacuum tank...

x2 on the vacuum tank.

Is it a part that has to be on the vehicle? the mechanic told me that I could just take it out?

Yes, it needs to be there. Well, that is if you like having your HVAC stay set properly or your 4wd stay engaged when at high throttle angles where vacuum in the engine drops. Of course that requires a properly installed & functioning check valve in the system as well. Vacuum diagrams are in the NV233 threads found in the tech article section.

But your mechanic gets to fix those problems when you have them so it's a win-win for him to recommend taking it out.

LOL.... good one. :)

thanks for the help much appreciated

The vacuum orb or canister is used to "store" excess vacuum so your HVAC, 4wd actuator have the needed amount of vacuum at high engine speeds to operate properly.
Like was said above, if it's removed the mechanic is just doing "job creation" because he's hoping he'll be the one to replace it for the NEW - no HVAC, 4wd problems that will arise.
It works in the reverse of an air tank on a compressor, same concept, just bassackwards.