Lets say you booked a call, and you are pushing the prospect down to close on the call, trying to overcome his objections, and it's just not working.
Take his number, and dial it into whatsapp, while being on the call!
If the prospect says: "I'll think about it"
Be like: "Could I get your number if you don't mind"
Then, add his number to a segregated list on whatsapp called "Follow ups", create this on your whatsapp.
4 days later, send him a DM telling him that your service could solve X problem that he is facing in Y timespan. Make it short and sweet.
If no response, follow up 4 days later with another.
This might help you book a follow up meeting, or make a sale.
Follow-ups can bring in lost dollars.