Objectivity is important in science because knowledge should be independent from the person.
Three to four decades ago there was a lot of discussion about objectivity. Especially in science this is important, because scientific information should be independent from time, place and person. The discussion ended up with the statement that though science and scientific knowledge are not 100% objective, however, there is no reason to strive for it.
In order to strive for complete objectivity, the scientist should stand back and be an observer of the things that happen in the empery. Now this is impossible, because the scientist is part of the empery. So the best thing he can do is to describe in detail what he has done. Things that matter can be placed in four interrelated parts of any research project:
What was the design of the research
Who (or what) participated in the research
What was measured and how was that done
Which analyses are performed.
A well done research describes these parts in detail. This is what is meant by methodological (= internal) validity.
Still some comments have to be made. First of all, the four aspects occur in any research, but they can be qualified differently in disciplines. Strong differences in the quality of a research can be seen in the visions of a qualitative and a quantitative researcher. And sometimes nothing can be recorded without manipulating or interfering the empery so simply wait and see what is happening isn’t possible.
Nowadays objectivity is replaced by replicability. This means that any research can be repeated over and over again, and the results should always be the same. Well, this might be the case in physics and chemistry (and only in special conditions), but this is far more difficult in social sciences (even in special conditions).