This is a personal choice and to some a bone of contention.
The sunleaves are little solar panels and batteries for the plant, collecting and storing energy.
Leaving them on the plant benefits it. EXCEPT for when it doesn't! :D
If you have a really dense canopy removing large sunleaves might be of benefit because of the clear space and airflow this creates. It also lets other growing shoots get light directly.
After a certain amount of growth upwards the lower parts of the plant are shaded out and will grow thin buddage @best. Some remove lower growth below a set level on the plant. This CAN be beneficial because it clears space for airflow, clears foliage which is unproductive and will eventually wither.
Its up to the grower to judge for themselves if or when one might remove sunleaves.
When I scrog I tend to remove big sunleaves from the vegging plant as they grow above or through the SCROG screen, This is to promote side-branching and light to the lower shoots. When I flip to 12/12 I will sometime during 'the stretch' period of the first 2 weeks since flip, remove all leaves and foliage from below the SCROG screen. This clears airflow so there is less chance of mold or bugs taking hold. It gives easy access to the plants under-canopy for maintenance also.
muA