I’m hoping to reduce lag in a game with lots of parts. I hope I can describe what I want here enough to not have to provide pictures.
I have 3 parts in the same line. The two on the outside are taller, whereas the one in the middle is shorter. they create a sort of door frame shape. Would it be less laggy to make one part and negate a door shape into it, or to use the three parts?
Using 3 parts is less laggy I think.
Would you say parts would be less laggy than unions in most situations or no?
If you’re using a ton of unions, I would go for parts. Unions are generally really bad for performance if used a lot.
I actually had this argument with a friend. I argued that unions where better but he proved me wrong after he showed me 2 blocks. 1st picture had the 2 block, not unioned or anything. 2nd picture had the same 2 block but this time unioned together. The union had 1-3 more tris then the separate parts.
Also union tend too corrupt easily. And if they corrupt you better have a OG backup, because if you don’t the union is gone. What happens is the part “exists” in the property tab but not in the 3d landscape.
tldr: only use unions if necessary. If you want to cut down lag, make it mesh since they ultimately have the lowest tris.
Nice reply! Better than mine is every way. I really think Roblox needs to fix the unions corrupting issue. I’m not sure if that’s out of their control or not. 
I agree with the corrupting issue, I shouldn’t have to worry about my saved unions disappearing the next day.
Yeah, considering the fact that when it happened to me, I was losing my mind trying to figure out what happened, and how to fix it. I was working on an airport at that time and the union that was corrupted was the runway, which as basic as it was, had a lot of time and effort in it haha.