There is no definitive answer to this question as it depends on the specific situation and yard. However, in most cases, using a tiller to level your yard is not necessary and could even do more harm than good.
If your yard is relatively flat and has few or no bumps or hills, then there is no need to use a tiller. A simple shovel or rake will be more than enough to smooth out the surface. However, if you have a lot of bumps and hills, then using a tiller can help even them out. Just be sure not to go too overboard with it as you could end up creating more problems than you started with.