If you don't use SikaFlex, the pilot hole is not an issue with the Avery style acrylic bits. The reason for the pilot is valid. If you want to drill through with no hole to match then use the acrylic bit to mark the hole, then no pilot may be needed. But if you try to hit an existing hole, the pilot bit allows some working room. I found that it was a little challenging to get the drill point perfect aligned with an existing hole. Like shooting fish in water - the plexi affects the visual aiming. Looking straight at the hole, and bringing the bit point to match on the surface, then standing up the drill square with the surface gave me the best results, but techniques may vary. Happy Building.
I should add, dipping the bit in water before drilling (slow rpm) each hole adds some cooling and a little lubrication. I completed another project with lots of plexi drilling and the produced cleanest holes. Relieve the down force as the tip penetrates the far side.
For the total DIYer