In general, when you obtain a temporary number you can forward it to a different number, such as your mobile phone or landline. The reason for this is to protect your privacy. Instead of giving individuals or companies your real phone number, give them a number that's exclusive to them. You can now get Chinese phone numbers easily via mobilesms.io/china-sms-verification/.
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In the future, if not to allow them to bother you anymore then you can switch it off, and the next time they call, they'll receive an "no longer available" message. One market that is targeted for these services is those who are single and don't wish to hand their personal number to someone they've seen in a club or at bars.
However, with some of the other services that can be linked to the temporary numbers of phones, they can be used for business applications too. There's an abundance of new services hitting the market, mostly internet-based, in some way that permit ordinary users to make new phone numbers active to give them out and then remove them at any time. The phone numbers can be programmed to ring to the number that is of the customer's preference.