When IS or NOT the correct time to install a fusible disconnect? Case and point...Ac just outside the window here has the non-fusible disconnect. Ac on roof at job has fusible disconnect?
Some AC equipment requires fuse protection. It should say on the nameplate of the unit if fuses are required. If not, than a non fused disconnect is permitted.
If fuses are required, and they are not upstream, you need to install a fusible disconnect otherwise non-fusible is allowed. Everything else is a design choice.