The answer depends on what sort of things you plan to build. Most of
the electronics companies I've worked for didn't have or need a lathe.

I've found the lathe most useful for making power transmission
components such as axles, bearings, shaft couplers and adapters, etc.
However these are often easier to buy than to make, unlike structural
components.

A mill can machine framework parts and drill accurate mounting holes,
so if you plan to buy the shafts and bearings the mill is enough.

Segway has a good machine shop with CNC lathe and mill but so far I've
been able to make everything I need here with the drill press, bandsaw
and belt sander -- to 0.1mm accuracy.

Neither machine is a substitute for the other except for very simple
jobs you could do almost as well with hand tools (and practice).

There's a Smithy Granite combo lathe/mill here in the shop that no one
likes. I'm told it is a very awkward milling machine and the plastic
gears break.

Personally I could live with a mill drill and 3"-6" mini lathe for
occasional light machining. Sherlines are just too small for my home
projects (log splitter, bucket loader, sawmill, etc) but I did use an
old 6" Sears lathe to drill pivot pin grease passages for the hydraulic
bucket loader and probably could have turned and threaded the pressure
relief valve with it.

jw