If you press the "Calculate" button a few times and then try switching any gear around it'll cause a ~1 sec lag spike, especially noticeable when you switch whole equipment sets. When you /reload then the issue is gone until you do more calculations, this was tested with all addons disabled except ReforgeLite.
I downgraded to narrow down when this happened and this behavior was introduced in v1.7.0, before that it was fine.

Updates are now dramatically throttled with v1.7.2. If you swap sets back and forth, it'll still eat up memory but it shouldn't be as extreme now.