Optimized the code regarding the beam projectiles leaving a fleeting beam behind them, however the count of deletions is still quite high despite this. 30-50 deletions per second.

Also fixed the code for evidence bags.

code/modules/DetectiveWork/evidence.dm

@@ -6,6 +6,7 @@
 	icon = 'storage.dmi'
 	icon_state = "evidenceobj"
 	w_class = 1
+	var/image/overlay_image
 
 /obj/item/weapon/evidencebag/afterattack(obj/item/O, mob/user as mob)
 	if(!in_range(O,user))
@@ -47,7 +48,8 @@
 	user.visible_message("\The [user] puts \a [O] into \a [src]", "You put \the [O] inside \the [src].",\
 	"You hear a rustle as someone puts something into a plastic bag.")
 	icon_state = "evidence"
-	overlays += O
+	overlay_image = image(O.icon, O.icon_state, layer, O.dir)
+	overlays += overlay_image
 	desc = "An evidence bag containing \a [O]. [O.desc]"
 	O.loc = src
 	w_class = O.w_class
@@ -59,7 +61,8 @@
 		var/obj/item/I = contents[1]
 		user.visible_message("\The [user] takes \a [I] out of \a [src]", "You take \the [I] out of \the [src].",\
 		"You hear someone rustle around in a plastic bag, and remove something.")
-		overlays -= I
+		overlays -= overlay_image
+		del overlay_image
 		user.put_in_hands(I)
 		w_class = 1
 		icon_state = "evidenceobj"
@@ -67,7 +70,6 @@
 
 	else
 		user << "\The [src] is empty."
-		icon_state = "evidenceobj"
 	return
 
 /obj/item/weapon/storage/box/evidence

code/modules/projectiles/projectile/beams.dm

@@ -1,3 +1,13 @@
+var/list/beam_master = list()
+//Use: Caches beam state images and holds turfs that had these images overlaid.
+//Structure:
+//beam_master
+//    icon_states/dirs of beams
+//        image for that beam
+//    references for fired beams
+//        icon_states/dirs for each placed beam image
+//            turfs that have that icon_state/dir
+
 /obj/item/projectile/beam
 	name = "laser"
 	icon_state = "laser"
@@ -7,46 +17,63 @@
 	flag = "laser"
 	eyeblur = 4
 	var/frequency = 1
-	var/ID = 0
-	var/main = 0
 
 	fired()
-		main = 1
+		var/reference = "\ref[src]" //So we do not have to recalculate it a ton
-		ID = rand(0,1000)
+		var/first = 1 //So we don't make the overlay in the same tile as the firer
-		var/first = 1
+
-		var/obj/effect/effect/laserdealer/lasor = new /obj/effect/effect/laserdealer(null)
 		spawn(0)
-			lasor.setup(ID)
+			while(!bumped) //Move until we hit something
-		spawn(0)
+				step_towards(src, current) //Move~
-			while(!bumped)
+
-				step_towards(src, current)
 				for(var/mob/living/M in loc)
-					Bump(M)
+					Bump(M) //Bump anyone we touch
-				if((!( current ) || loc == current))
+
+				if((!( current ) || loc == current)) //If we pass our target
 					current = locate(min(max(x + xo, 1), world.maxx), min(max(y + yo, 1), world.maxy), z)
+
 				if((x == 1 || x == world.maxx || y == 1 || y == world.maxy))
-					del(src)
+					del(src) //Delete if it passes the world edge
 					return
-				if(!first)
+
-					var/obj/item/projectile/beam/new_beam = new src.type(loc)
+				if(!first) //Add the overlay as we pass over tiles
-					processing_objects.Remove(new_beam)
+					var/target_dir = get_dir(src, current) //So we don't call this too much
-					new_beam.dir = get_dir(src, current)
+
-					new_beam.ID = ID
+					//If the icon has not been added yet
-					new_beam.icon_state = icon_state
+					if( !("[icon_state][target_dir]" in beam_master) )
+						var/image/I = image(icon,icon_state,10,target_dir) //Generate it.
+						beam_master["[icon_state][target_dir]"] = I //And cache it!
+
+					//Finally add the overlay
+					loc.overlays += beam_master["[icon_state][target_dir]"]
+
+					//Add the turf to a list in the beam master so they can be cleaned up easily.
+					if(reference in beam_master)
+						var/list/turf_master = beam_master[reference]
+						if("[icon_state][target_dir]" in turf_master)
+							var/list/turfs = turf_master["[icon_state][target_dir]"]
+							turfs += loc
+						else
+							turf_master["[icon_state][target_dir]"] = list(loc)
+					else
+						var/list/turfs = list()
+						turfs["[icon_state][target_dir]"] = list(loc)
+						beam_master[reference] = turfs
 				else
 					first = 0
+
+		cleanup(reference)
 		return
 
-/obj/effect/effect/laserdealer
+	proc/cleanup(reference) //Waits .3 seconds then removes the overlay.
-	name = "laserdealio"
+		src = null
-
+		sleep(3)
-	proc/setup(var/ID = 0)
+		var/list/turf_master = beam_master[reference]
-		sleep(5)
+		for(var/laser_state in turf_master)
-		for(var/obj/item/projectile/beam/beam in world)
+			var/list/turfs = turf_master[laser_state]
-			if(ID == beam.ID)
+			for(var/turf/T in turfs)
-				del(beam)
+				T.overlays -= beam_master[laser_state]
-		spawn(0)
+		return
-			del(src)
 
 /obj/item/projectile/practice
 	name = "laser"