Simply put, Max Clicks can sometimes burn through budget, raising your CPCs and CPAs. This is true of any new bidding strategy in the short term due to the learning phase, but Max Clicks is seems to be particularly aggressive in ad auctions. To put it another way, you probably won’t fail to spend your full budget if you’re running Max Clicks - Google will find a way to spend that money.
This is particularly concerning since this bid strategy doesn’t have an underlying goal of getting you conversions at a certain volume or CPA. You’re able to place a limit on the CPC you want within this campaign, but even this has proven less effective than a proper implementation of tIS.