CPM and CPC both methods have its own merits and demerits. CPM bids are kinda cheaper than CPC bids. Hence when you are sure that your CTR’s will be very high, then it makes sense to go for CPM based bidding. Mostly the offers kinda campaigns are done using google display with CPM bidding. For Example: Uber’s/OLA’s first free ride campaigns. At other end when your objective is to get actions then it makes sense to go for a CPC based bidding strategy. So that you pay for clicks and clicks come when there is an intent.