with agblk = 0, the allocation of AGCH is dynamic : it can be 0, 1, 2 blocks, or more if needed, depending on the demand.
If you set agblk = 2, then this is static. The allocation of AGCH cannot exceed 2.
Normally, by setting a dynamic allocation of AGCH (agblk = 0), you maximize resources for both PCH and AGCH, so this is an improvement.
However, if you’re still experiencing PCH blocking, then you should consider reducing your LAC size.