How can the "real practice" possibly be harmed by a deeper understanding
of the language?

Regardless, it's much more important to understand the problem domain
(business, engineering, genetics, gameplay, whatever you're going to be
developing for) than it is to understand every detail of a programming
language.

Hi,

I did the SCJP exam specifically to learn the language (I didnt have
much experience with JAVA before) and it has definitely helped me and
made me feel more confident.

I can't say that having the certification on your CV will help you; it
depends on the company and the agents that you use to find a job (not
everyone knows what an SCJP is and some are more interested in years
experience or Tertiary qualifications).

I like to think that having the certification on my CV means that a
possible employer will give it a second look because it shows that you
are making an effort to enrich your skill set and knowledge.

Chris