Can someone help me understand?

I was just curious why a longer primary is really beneficial? why is it better to primary for 3 weeks and then bottle and wait 3 weeks instead of just primary for a week or 2 and then wait in the bottle for 4 or 5 weeks? what happens in the primary that doesnt once its bottled?

It really only matters for bigger beers and lagers that actually take a while to ferment. For most ales, you can bottle as soon as the SG stays the same for 3 days. I have drank several of my beers within 3-4 weeks of brewday.

there is a short answer, and a very long technical/chemical answer.

the short answer is that during fermentation the yeast produce a myriad of chemical by-products in varying amounts depending on a variety of conditions as well as yeast strain. When primary fermentation has neared completion, the yeast begin to then metabolize their own waste as well as produce even more waste which will react with previous waste to break it down.
if the yeast are not given time to clean up their own mess, you can/will taste it. there are plenty of ways of helping to reduce these compounds mechanically and chemically, but it is mostly not useful for a homebrewer. for that, a nice long primary is best.

longer exposure to the bulk of the yeast will aid in breaking down fermentation byproducts.

Then use gelatin in the secondary to clean that crap out.

ok. well i understand fully that a longer primary before bottling makes for a BETTER beer, but due to some time constraints, bottling a week old beer will still result in something tasty correct? Ive never bottled anything earlier then 2 weeks before, but I need beer quickly and want to make sure I can still have good young beer.

how good a beer will be young depends on 2 things, IMO: style, and your pitching rate. if you pitched really well, and had a nice full fermentation pretty quickly, and the style does not rely on the break-down on harsh by-products (i.e. Imperial Stouts), then you will have a better shot at having a good bottle.

the beers I want to bottle are just simple SMaSH brews with 2-row and they are small batches, only 1 gallon with a full packet of dry yeast used on each of them.

well, I would say that you have a good chance of them being decent. i am sure that they would improve with time, but if you absolutely must drink them now, then it seems time is more important than taste for these batches.

Well they are small beers with large yeast pitches, simple malts and low SGs so im sure they will be decent. keep in mind I would never usually bottle a beer after a week in primary normally haha, but my brother is coming in 2.5 weeks and I just want to make sure I have beer for him when he gets here. I have a 4 week old Blonde Ale 5 Gallon in the primary right now that will be available on tap when he gets here but I dont think its going to be enough and just want soemthing extra hanging around haha. At least I know the majority of the beer he will be tasting will be aged well