i've made some test on this for my current project ("Space Tako Invasion")
for exemple on trail missile or explosion (destroy when animation finish using a famillie)
And using a classic create/destroy technic with a fade behavior + outside the screen.
the problem with this technic is that increase a lot the number of objects in Construct2 and this is doom completly the perf on mobile (test on a my galaxy note 10.1 tablet).
I test a simple pool managing system with a variable ("in_use")but the problem is that i need to select all and manage the variables so this isn't efficient too.
For particules the most usefull and fast was the particules system of construct2 1 object for all the particules trails, you only need to know that if you destroy particules object you will destroy the instance so all the particules (of your trail for exemple) will be destroy too (just manage the time before destory and that will be ok).
<img src="http://www.angelsoftware.fr/wp-content/uploads/alpha_04.png" border="0" />
the last test i've done it for the my other game test "Coffee Time"
i use trigger on map to make 2 test :
1 - the trigger just initialisate a variable ("active") to make the ennemies ia active (move, ect...)
2 - the trigger create object ennemis and the ennemies spwaner on the map.
the 2 test was really bad on mobile with cocoonjs because when i create object i thing the allocate of memory is done and i notice freeze.
it's only appear if you've have big gfx.
So depending of the size of the gfx and you're need, a simple variable is a better way to manage ennemies on level.
for dynamic and fast object (low gfx size) if it's just particules use the particules object.
If it's for exemple fire, use create/destroy.
<img src="http://www.angelsoftware.fr/wp-content/uploads/coffeetime_prototype_level.jpg" border="0" />