What are the advantages and disadvantages of taking an Erasmus exchange semester abroad, and will it have an effect when it comes to finding a job?
Going for an Erasmus, an EU student exchange progamme, may be a plus, not only "the obvious cultural advantages" (like learning a language better than in the lab / during holidays) if you watch out for similarities and differences in your field, comparing your home and your hosting institution. Hopefully you will recognize both the odds and the benefits of different teaching / learning cultures and mint benefit for you. Use it as a chance to learn differently, including different topics than at home.
If possible, look for integrated programmes (like the ones by the French-German University, for example), where two institutions are partners who mutally agreed on the curricula. Otherwise upon your return, if there is no recognized equivalent of what you did at your host institution at your home institution, you may have to attend lectures and lab classes a twice and hence, delay completion of your studies.
Going for an Erasmus is a potential obstacle, be prepared some won't understand you this well anymore, as your horizon of experiences may diverge from theirs. At your host institution, at least at the beginning, you will be a foreigner; at your home institution you may be earmarked as "thinking different" or "s/he once left the boat". You may somewhat "tainted" like a foreigner, or become a pacemaker returning with new ideas.
Is it better for getting a job? Again, it depends on the where you want to go, if the potential employer recognizes, appreciates and supports the benefits of someone who left the nutshell. Some do their studies including a PhD and beyond, promptly find a job, never even thinking about getting into an Erasmus; all staying in the same city. Some face the difficulties of "you no longer think/act as we expected as a true/pure (insert your nationality) physician / biologist / .... would do."
Other answers aren't wrong, but I think an important point is where you are going to search for a job upon graduating. If you are going to work in your own country in a job not related with international relations, an Erasmus may be just a plus, as Buttonwood says.
However, if you plan to work abroad an Erasmus may be a very useful experience, specially an Erasmus in the same country you are going to search for a job. It can be useful both to gain skills to live and interact abroad (that can be shown in a resume) and to test if you are suited for the experience of working abroad. In addition to that, an Erasmus in the last years of your studies is an opportunity to start networking in the target country.
Furthermore, in countries where professional proficiency of English or other foreign language can't be taken for granted, an Erasmus is a good practice and a good evidence of your language skills.
I've meet an Spanish engineer working in Finland after an Erasmus in Finland and a German engineer working in Spain after an Erasmus in Spain, and as far I know the Erasmus were an important step in deciding to work there and in finding a job there.
To summarise in two examples: for an UK student planning to work in the UK, an Erasmus would be just a plus; for an Spanish student planning to work abroad, an Erasmus would likely be a must.
While in general, studying a semester abroad will likely make a positive impression in your CV (even if you 'lose' half a year on the way), I have experienced that some of my colleagues would regard an 'Erasmus' stay slightly less valuable as opposed to organizing your foreign semester all by yourself (outside of such a program).
I am not going to say that it is particularly 'easy' to go abroad with Erasmus, but I think this sentiment originates from the perception that some Erasmus students primarily get in contact with other Erasmus students (e.g. from their home country) and not so much with their local peers and local culture. This is of course strongly dependent on your own dedication and in general may just be a prejudice.
Overall I'd say, studying abroad with Erasmus is still much more valuable than no foreign cultural experience at all.