It really depends on the design. Hot sport models will and usually do fly with just aileron and elevator input and look fine. As the speed lowers, like for landing or during very slow flight, some rudder added in with the left thumb will help smarten up the response and also help to avoid a tip stall.

Other models that use higher aspect ratio wings and/or have higher camber wings will benifit from coordinated use of rudder and aileron. Gliders are one good example and some other scale models gain a lot from some coordination as well.

But in all cases the amount of the mix changes with flight speed and intent. So learning to deal with it is part of the skills you will aquire. So stick with independent controls.