The premise of the incumbency effect is that there are advantages to being an incumbent which puts challengers at an automatic disadvantage. The effect suggests that "the incumbent always wins." Its effect on members of Congress is to recognize that once office is gained, a natural set of advantages comes with it for reelection purposes. This is especially so in the House of Representatives:
"The electoral advantage of incumbency is perhaps one of the best known and least understood facts of American political life," Abramowitz wrote. "Nowhere is the advantage of incumbency more clear than in elections for the U.S. House of Representatives."
Since elections in the House of Representatives are every two years,the incumbency effect is most pronounced there. Elected representatives are able to argue that they are listening to the voices of the voters, but "change takes time" or that "they are working on the problem." The ability to appeal to voter patience as well as generate funding for reelection campaigns with relative ease and generate consistent name recognition in a small window enables the incumbency effect to be present.
An advantage is that what some incumbents claim to be the case might actually be so. For example, if a Representative has been in office for two years and is making strides towards significant change, they should be given more time to make their vision a reality. At the same time, this can be used as a stall tactic, a mechanism to enable the elected official to have more time in office at public expense. Term limits has been one element proposed, but doing so would require a change to the Constitution.
Part of this is cyclical. There are moments in American History where being an incumbent is not a good thing. For example, being in office during the 2008 election, a "change" year, meant that incumbents needed to be on their guard. This was also seen in the midterm elections in 2010 where the incumbent Democratic party "took a shallacking" in the House and the Senate. In these moments, being an incumbent did not stop the intense call for change. Perhaps, this is where the reality of the incumbency effect is seen. When the call for change is heard and resonated by many, the incumbency effect is not necessarily persuasive. By the same token, if the current state of reality is functioning well, "If it ain't broke, don't fix it," then the incumbency effect might be a condition that is reflected in political reality.