Whether you travel a lot or once a year you will always need a return ticket. It is required for getting a visa and entering a country even if it’s visa-free. Also, airport employees can request your return ticket while you check-in for a flight. That has to do with the fact that if you are detained in another country due to the absence of a visa or a return ticket, all costs for your deportation will be borne by the airline you arrived in the country. In the understanding of the immigration service, a "return ticket" is a ticket to any country, not necessarily back. Such tickets are also called tickets to a third country or onward tickets. Moreover, some countries demand travelers to have them.
ATTENTION! There is a risk that you will not be allowed into the country or denied a visa without a return flight!
Of course you can go to another country without any return ticket, but the chances that you will be admitted to the country are very small. In this way the result will depend more on the mood of the particular employee and your ability to negotiate. There won’t be any issues if you have a return flight from the country. Apparently, the date of departure must be before the expiry of the period of stay in the country.