One powerful reason why you generally want to avoid having a meter running is you are really making two related but distinct sales: you are trying to convince them to pay, yes, but you are also trying to convince them to use your thing versus their existing way of doing business. That is often the harder sale. Putting a marginal cost, even in free quota, for using your thing puts friction in the adoption process, which you KEENLY do not want.
While it may be the case as a bootstrapped entrepreneur that your business has not yet spent the sum of $600 on everything put together, the overwhelming majority of businesses are not like you. Many businesses will spend $600 today on one line item, for instance virtually any company which employs 3 or more college graduates. Many of these businesses also have habits with regards to buying software which are more beneficial to SaaS companies than your habits are, for example a) having predictable positive ROI on integration costs and b) never attempting to optimize for $150 expenses by switching providers on a whim.