The quick answer is that Google Analytics is tracking similar but different things than Lead Gen & CRM Ads, in similar but different ways.
Example: In your Lead Gen & CRM Ads dashboard, you might see 4 conversions tracked yesterday. That means that a conversion goal you created fired 4 times for people who viewed or clicked one of your ads.
Meanwhile, in Google analytics, just 3 conversions are attributed to Perfect Audience yesterday.
When comparing numbers like this, first check that the conversion goal in Google Analytics is tracking the exact same thing as the conversion goal in Lead Gen & CRM Ads. If they're not, then discrepancies can occur.
Second, it's important to understand that while the Lead Gen & CRM Ads conversions are counting people who clicked on or viewed ads, Google Analytics is counting people based on the content of the URL parameters in the pages they load as well as other factors.
While these two methods of tracking often show similar results, they are tracking different things differently, so discrepancies occur. For instance, it's normal for the click count from an ad campaign to be a bit lower than than the attributed visitor count in Google Analytics. This is because clicks are not visits. They are different things, tracked differently. In fact, Google itself tells Adwords advertisers that numbers will not line up between Adwords stats and Google Analytics stats...and they built both products! The issue is so common that they've written detailed explanations and even made a handy matrix with reasons for each common discrepancy across their marketing products.
Solution: The best way to confirm the ROI of your Lead Gen & CRM Ads campaigns is by using our many conversion attribution tools to get actual info about the sales generated and users signed up by your ad campaigns. Lead Gen & CRM Ads lets you pass sale and user data into our site tracking tag so you can attribute each individual conversion that happens to data on your side. In this way, ROI can be measured transparently and easily.
You can learn more about conversion attribution tracking in our documentation.