Regarding "unnecessary lag": if the sole reason for a tile entity is for rendering, your TE does not need to tick and thus won't produce any lag.
Technically, the presence of any tile entities in a chunk mean a little more work to load the chunk, but if you have enough instances of your TE in a chunk to cause loading performance issues, then you probably also have enough to murder client performance with all the rendering that's going on.
tl;dr non-ticking tile entities produce zero lag unless you grossly abuse the feature.