Do you really want to flatshare ? In London its usually the only way because self-contained property and accommodation (i.e. with just you in it ) is prohibitively expensive. However people want to share a property for all sorts of reasons. It may be you’re new to London and new friends would be a bonus.
OK hit 'pause' here. Your flatsharers can’t be your only friends. You are usually expected to have some previously installed in your life prior to moving in.
Sharing with people from overseas can be good in several ways, i.e. being getting invited back to a holiday destination and staying there for free. There is of course learning a language, cultural experience etc.
Some people just want to sharea flat or house. For quite a lot of people, the flatshare is a makeshift family without the need to 'do' Christmas: providing a bit of mutual list in a big bad city. Actually its usually the ‘bad’ in ‘big bad city’ that people come for in the first place.