One mistimed standing tackle can leave you exposed at the back, and that's super-dangerous on the higher difficulty levels, especially against the better teams. Here's a general rule to follow in such situations: right before the opposing player sets himself to cross, take him out with a slide tackle.
It might sound cheap, but it's ten times better than letting that ball into the area and running the risk of a headed goal.
Headers are pretty over-powered in this year's game, and that's true of the CPU teams too. If they manage to snap a cross off before you manage a slide, there's probably an 8/10 chance it's either nestling in the net or going for a corner. That's why smashing them is a better tactic.
Who cares about giving away free kicks when it could save a goal, right? That should be your thinking here. For some reason, free kicks out wide don't cause as much panic defensively as crosses in open play or even corners. Keep that in mind.