I import a lot of files in either Step or Parasolid and have so for many years. The actual import part seems to work as expected in 2018 but what happens after looks like it has gone downhill big time, well at least for me anyway.
Firstly removing appearances works initially but say you open up a assembly a day later somehow they have reverted back. Doesn't seem to always happen but happens too often. Before closing I rebuild and save all so when reopening they should be how you last left them
Secondly and this is the big one (this is random) Solidworks loses all association with the imported body - note body not part file. This can range from frustrating to a total disaster. I have done tool designs and opened them up the following day and all association to the bodies in the splits is lost. So that can take ages to fix then all what happens after in building the full tool is also killed which also takes ages to fix.
And it doesn't just apply to the parts you created the split - all the ancillaries you may import in may die that may mean reassigning mates or much worse.
Again like appearances I rebuild and save all before closing and all is good...………. until later. Or you may go into the imported file change a fillet rad come out and low and behold nothing recognises the body again in the cavity split/assembly
Now you live with the odd problem on imports it is to be expected but these problems (especially the second one) has put me on tender hooks. I just never know when it will happen.
I'm on windows 10 and solidworks 2018. 2017 seemed reasonably fine (ok you got the odd bug as I remember on imports but not to this extent)
Of course it could just be my set-up causing these problems. Hoping to hear some feedback. Been down the road of removing reloading in past just to find out later it is the software not my rig.