When doing partial boil, does amount matter?

Curious if it matters if doing a partial boil, you boil say 2 gallons or 4 gallsons, will the end result be any different? If so, why? At the end the day, you hope to ferment ~5 gallons, so I don't get how boiled amount would matter at all, no matter what you boil, it will be dilluted to 5 gals right?

It does matter. Smaller amount boiled will lead to more carmelization of the extract and a darker color. Even more important than that, with smaller boil you'll get less bittering from your hops because of the higher gravity.

Imagine trying to fit 6lbs of malt into 2 gallons of water and boiling for an hour, you would pretty much be back to LME but a lot more carmelized.

Hops won't be utilized nearly as well like Iowa said.

Check out on of the brew programs to see what the difference REALLY is. I use brewsmith and they have a free trial so you can check it out, works great for me.

The two above hit it on the head. You can still make good beers from partial boils (I often only boil 1.5g), but it is difficult to get a light color without late extract additions. Further, you can only get the beer so bitter with such a small boil. You can make up for lower hop utilizations by increasing amount of hops or length or boil (or doing a late addition with only hops in water for the first 30 minutes). On hop utilization though, ultimately there is a maximum (I believe 90IBU soluable into a solution for a 5% beer) limit; thus once diluted you would be decreasing that(i.e. 90IBU max in 1.5g dilutes to 27IBU in 5g). You can make up for this by brewing the recipe in 1.5-2g and brewing a hop tea with another 1.5-3.5g (i.e. hop just water...). I'll post a link to a post on this last subject.

In short, a full boil is the way to go, however good beer can be made (just not as easily) from 1.5g boils...

Look up hop utilisation.