I seldom close the cover on my machine (where the spools are).
But I ALWAYS use thread nets on ANY spool of thread I use on
my machines.
I have found that the thread nets help "control" the unwind of
the thread as it is sewing or stitching embroidery.
Of course this is just what I have found works best for me.
A few years ago I was having issues with my thread (ALL thread
not just embroidery) was nesting in the bobbin area. What I found
was a SMALL mess of thread in the upper tension area. What I did
to remove that (without taking machine apart or in for repair) was
take a LONG length of 6 strand embroidery floss and "thread" it in
the machine without going threw the needle and pull it out from the
bottom I did this repeatedly until I was able to 1) work the "nesting"
of thread out or 2) able to get some LONG thin tweezers in enough
to grab the thread and pull it out (if you can see anything).
Now before I start ANY new sewing project I run the floss through
the machine just to "clear" and thread pieces that might be in there.
So far no more issues with nesting in any of my machines.