Conditional Revise option is set Enabled by default since it meant to optimize the synchronization process. Let’s see how it works.
When the option is Disabled, M2E Pro revises all the smallest changes to Product Price. Yet, updating the minor changes to the price values (e.g. from $25.90 to $25.99) most likely has no practical effect, while may overwhelm M2E Pro servers. In this case, more important price changes (e.g. from $25 to $50) may stay in a queue instead of being updated immediately. As a result, you may face a revenue loss.
To avoid the issue, it is highly recommended to keep Conditional Revise option enabled. For example, you can set Revise When Deviation More or Equal than option to 3% and M2E Pro will revise your products in realtime format only when Magento Price is deviated by 3% from the initial value. This way you’ll make sure all the important Price changes are detected and revised on time.