As Hokie66 says, it depends. Size, complexity, budget, contract requirements, schedule, site location, etc. Also consider do you need to be making weekly field visits for during the entire project?
Once foundations are poured and structural framing complete, does the structural engineer need to be go out to inspect application of gyp board on the walls? Likewise, the HVAC engineer does not need to watch foundations or slabs being poured.
For example a plumbing or electrical engineer might make several visits early to inspect underground utilities before they are covered. Then go several months without a visit while foundations and slabs are poured and structural framing erected.
If a job site is on the other side of town, weekly visits are easy to do. However if the site is in another state (I have one project going in Charleston, SC with the engineer out of Kansas City, MO), weekly visits becomes costly so you might be limited to visiting once a month.