I think almost everyone syncs everything. It's totally okay to do, but is also highly dependent on your lead assignment rules/the way your business uses SFDC and Marketo. I tend to keep the Marketo profile in SFDC the owner until they reach their scoring threshold, then they're assigned through the SFDC rules.
However, if you're not able to do this, your reps will see leads before they are ready/have reached their threshold unless you're using predictive lead scoring. If you have a sales team that doesn't jump the gun/doesn't hunt for leads in SFDC, then it's probably okay to sync everything. If not, you may want to hold them in Marketo until they've reached their MQL stage, then sync them into Salesforce. The flow for this would be "Trigger: revenue stage is changed, new stage is MQL" then "sync to SFDC" in the flow. Using the modeler makes lead routing/holding things back in Marketo markedly easier than without using it.