The overlapping UVs issue you’re having is that the generated Lightmap UVs that the editor does just repacks the UV channel 0 (texture UV). This takes the existing UV islands and spaces and stretches them to utilize the majority of the 0,1 space for your lightmap UV.
It does not create new seams for your existing UVs. For instance, if you create a cylinder mesh in your modeling program and do not break apart the faces into their own UV islands (ie a rectangle and two circles) the generated UVs in UE4 will not do this.
The truth of UVs is that they can be a time sink, but it’s a major process in 3D modeling that is a necessity. The auto generated UV can save you a bit of time if your texture UV has already been seamed and separated in a manner that fits within the limitations of the system.