Personally, I don't see any need to converse in English if we share the same non-English mother tongues, say Mandarin, Bahasa Melayu, Tamil, Cantonese and so on.
Well, chit-chating with friends in English doesn't necessarily improve your proficiency in English. Instead, by gradually conforming oneself to the Malaysians' way of speaking English, although you may speak more fluently, but, at the same time, your English might drift further away from the "real-English" spoken by most of foreigners out there.
First, I think we have to really understand what's the main purpose of learning English. To me, it's a medium or "bridge" to get our ideas across to those who cannot comprehend our mother tongues such as Mandarin or Bahasa Melayu. If you agree with this statement, question yourself, what's the point to speak English (or Manglish to be more accurate) with your friends? Afterall, conversation is just a transfer of information or ideas, if Mandarin or BM serves better in communicating with friends, what's the need to speak English?
Well, I suppose you might argue that we need practice to speak better. I concur that. But, speaking with our local friends is definitely not an effective way of practice. As I've said earlier, such practice profoundly degrades your proficiency.
Consider the following example:
"Hi, this is my wife, she is thirty, I am thirty two."
our Manglish or Singlish usually sounds:
"Hi, disc is my wife, she is dirty, I am dirty too."
this is just one of the numerous examples of how disastrous it actually is. Well, you might take pride of it as a national identity or cultural uniqueness or whatsoever bs. But, come back to the main point, if you see English merely as a communicative tool, please don't take speaking English with your friends as a means to improving English.
Well, I'm not really good in English, but if you ask about my opinion, this is my opinion...