If you're an expatriate (student, employee, self-employed, globetrotter or pensioner) and not just temporarily posted abroad, you will no longer be covered by your home country's healthcare system, and will probably have to contribute to the local healthcare system. However, this does not mean that your healthcare costs will be reimbursed at the same rate, or even that you will benefit from the same level of coverage when you return to your home country. The cost of healthcare varies considerably from country to country, and can be much higher than what you're used to paying at home.
If you only join the local social protection scheme in your country of expatriation, your reimbursements are likely to be limited or non-existent, and you won't be covered while traveling or when you return to your home country.