Singaporean Long Term Pass visas (such as Training Employment Pass, Student Pass, etc that allow you to go through automated border control clearance) state that the biometric visa card must be surrendered when it expires or when a new one is issued; otherwise, it technically counts as an overstaying offence if you come back to Singapore. Is this rule enforced strictly? I will be flying out of Singapore before my long term pass expires, but I might come back in a few months for work or travelling.
There are 2 types Long Term Visa Pass:
LTVP that issued by ICA (Immigration Checkpoint Authority)
You don't need to surrender this pass. This Pass has an overstaying period of 30 days. If this card expired, you would still be allowed to stay 30 days and won't be penalized. If you still stay more than the grace period, upon leaving Singapore you will have a penalty fee or charge.
LTVP that issued by MOM (Ministry of ManPower)
LTVP is issued if you are a spouse / child / relative of the Employment Pass owner. It's fine not to cancel this LTVP. Upon the cancellation of the Employment Pass, this LTVP will get a Cancellation too. In case you need to fly out of Singapore but need to return to Singapore before the pass/card expires, please KEEP the card. There is NO NEED to return this. Upon expiry of this pass, you are still allowed to stay 30 days but after that, you have to pay a penalty fee or charge.
In summary, there is no need to surrender your pass.
Note that Training Employment Pass (TEP), SVP (Special Visit Pass), LTVP (Long Term Visit Pass) and LOC (working pass for LTVP) are totally different.
In case you are flying out of Singapore before the term of a long term visa expires, you can surrender your card when going through the immigration checkpoint. Request a surrender of card form from the immigration officer and fill in cancellation request detail as 'leaving Singapore via flight/bus/boat X on Y'.
There are friends of mine who don't plan to come back to Singapore who were told by nice immigration officials that they may keep the LTP visa card as a souvenir. Technically, this is illegal although it doesn't affect you if you don't plan to come back to Singapore. If you do, then not surrendering your card the previously counts as an overstaying offence.
If your long term visa expires, then you have seven days to cancel the card. The exception is that if you are being issued another long term visa card within a fortnight of the previous one expiring, then you can surrender your existing card when the new one is issued. I did this, and thankfully I had retained my previous card as I was told by the officer that if I hadn't handed in my old card when I got the new one, that would've counted as an offence too.
EDIT: Just to clarify, I'm not talking about a Long Term Visit Pass, which is different. I was referring to the other passes mentioned in the question which also count as 'long term passes' when passing through automated clearance gates at Singaporean borders.
EDIT 2: I've heard from students who didn't surrender their student pass and didn't have a problem when visiting Singapore again. If you really want to be sure, you can also send your Student Pass via postal mail back to ICA.