In aid of legislation

A most common excuse for having senate- or congress-level investigations to high profile issues is doing it "in aid of legislation."

In my limited political knowledge based on my decades old high school history lessons and college political science classes, I assume that the senate and the congress are elected to represent the interests of their constituents.

The Senate of the pre-clone war Republic in the Star Wars franchise shows a chamber of representatives from various planetary systems, special interest federations, and alliances. This gave me an idea that the senators are there to ensure that the rule of law is respected and adhered to by all members. They are also there to defend the actions of the entities they represent and raise and settle any disputes between bodies represented in that senate.

According to my mental notes, both the senate and the congress are tasked to craft laws that will strengthen declarations embodied in the constitution. Being the representatives of the people who voted for them, they have the obligation to look into the effect of the laws being crafted and make certain that it does not in any way negatively affect the rights of their voters.

For three years the budget has been reenacted because of senate or congressional "investigations in aid of legislation." For three years the people made do with what the government allocated for basic services. For three years the problem of adequacy of resources was set aside.

I was not able to do much research but what legislations were aided by those investigations? Was the government able to get back the money spent to keep the investigators comfortable during the deliberations? Did the people gain anything from those investigations?