They will charge you an annual fee – or in my case, deduct my hard-earned UNI$ – and refuse to reverse the deduction unless you cancel one of them.
I had a UOB Preferred Platinum Visa and UOB Amex for 4 years with no issue, and got the fee waiver every year, except this year when they ABSOLUTELY REFUSED to give me the fee waiver and forced me to cancel one of the cards in order to get the UNI$ deduction reversed. 
Though to be honest, the UOB Preferred Platinum Visa is only good for collecting points if you pay via contactless mobile payments anyway. And if you do a lot of entertainment spending, which I don’t (and with COVID now, who does?).
For shopping and everything else, I either use my OCBC Titanium Rewards or DBS Altitude Visa.