Beware tho - even if they look like effects, they're still units. That means they take more processing power than special effects because they're still units (due to how more complicated units are compared to special effects).
Just for comparison, I made a spell for my map which caused a meteor to drop down. When it crashed into ground, it exploded and created ~40 small fires in the area it affected. With those fires as units, I experienced some serious fps drops, although the code was cleaner (did not need any loop, I just set them correctly in object editor and assigned timed life to them upon creation). When I remade the trigger and just used special effects instead of units, those fps drops disappeared. Of course the trigger I had to make was more complicated as I cannot give timed life to special effects, so I had to keep track of it myself.
So probably a few units that serve as graphical effects ain't that bad, but if you want to spam many effects at once, you should consider scaling the model via some 3rd party tool like chaosy wrote and use them as special effects, not units.