Wastegates are not essential. Many of our combinations don't use them. They come into play when you are trying to use a smaller turbine housing/wheel for low end performance. As bmoeller said, if your boost levels get to high, shaft speed it too high or back pressure is to high, then a wastegate is a good idea.
If you don't have room, then a larger turbine housing or wheel will help at the loss of some low end performance.