I use Cursor and I usually put it in plan mode and feed it the specs so I can review the plan and make sure the implementation will be done the way I want it to or to make sure the plan "feels" right.
When I hear or see that people feed the specs, let agents handle things and then do some quick tests to make sure things work as expected, that sounds way too risky. I still have bad experiences where the agents made bad assumptions and included things I didn't need or ask for or had to stop the agent during implementation because it was going down a path that was needlessly complicated.