According to Act No. 121/2000 Coll. on Copyright, you are obliged to state information about the source from which you took over a thought. When citing you need to proceed prudently and distinguish whether it is actually someone else’s original thought or a commonly known fact in the respective field.
For example, a physicist mentioning Archimedes’ Principle, unless it is a subject of his research, will not refer to the original source, because it is now a widely known fact not only in this field but also in secondary school. However, should Archimedes’ Principle be the subject of his research (e.g. a comparison of its definitions over the centuries), the source must be given.
You can intensify the strength of your ideas or conclusions by using so-called argumentation by authority and refer to publications written earlier by other scholars, especially those widely-recognized in their field. You also cite to complement your idea or develop it further.
You also cite if you want to disprove someone’s idea. In this case, you should always give the information you want to disprove, either by citing it word for word or paraphrasing it (i.e. briefly retell the original idea in your own words).
Correctly created references to the sources used will enable readers of your text to identify the documents from which you drew your information. Not only can readers verify whether you drew on this the information accurately, but it will also save them some work when searching for publications for their own similar topic.
Citing may help when finding out what connections there are between individual authors as well as when and who they cited. In this way, you can ascertain whether a specific research issue has been discussed by the same authors in a circle, or who dealt with a particular line of research in the past and how authors followed each others’ ideas during their research.