If you weren’t aware, in the original manga of DB, only Vegeta attacked Cell during the Kamehameha clash between Gohan and Cell.

The Z-Fighters attacking Cell is anime-only content. The filler here enhances the scene and makes it superior to the original. It makes sense that the Z-Fighters would intervene instead of doing nothing.

Especially, Piccolo, who was willing to put his life on the line to save Gohan when he was being crushed by Cell earlier. I appreciate the little monologue that each of the Z-Fighters delivers while attacking Cell. Krillin, Tien, and Yamcha all reflect on how Goku has shaped their lives and changed them.

Their efforts to help Goku‘s son is their way of thanking him. The reaction shots we see from Dende and Chi-Chi highlight the severity of the situation and add more tension to it. It makes the scale of the event more bigger.

It’s great to see more spotlight on the side characters in this scene. It makes it more epic and iconic. Additionally, Vegeta being in his SSJ form when attacking Cell is better than him being in his base form. This is a great case of good filler. 

The Anime Having the Z-Fighters Attack Cell During the Beam Struggle is One of the Best Changes to the Series