Is there a need to always check for plagiarism?
Being certain that you quote correctly is pretty straight-forward (if it's not your words, use quotes), but learning to paraphrase well is difficult for some people.  I think this may be more often the case for those who are not native English speakers: my observation may be less about language than about differences in educational culture.

For a person who doesn't have confidence that they are paraphrasing sufficiently differently for typical scientific writing standards, I could see that running through a plagiarism checker might be useful as an educational tool.  Much more effectively, however, such a person might want to work with a trustworthy writing service (most American universities provide something of this sort free to their students) to get an independent evaluation of the quality of their paraphrasing and help in improving it if needed.

Once you have enough experience to be confident in your ability to paraphrase, however, I would not bother to do any sort of double-check unless you have an extremely nervous personality and it will help you to sleep at night.