Is it necessary to remove sprite sheet after scene change? spritesheet:dispose();

spritesheet:dispose();
spritesheet = nil;

is it necessary to remove?
I found that I got nil error sometimes when I use spritesheet:dispose();. I feel like
table.remove(group, i) is handle about this…?is it correct?

I want to improve my app performance, any suggestion?

(I use scene manager class not director class)
[import]uid: 65906 topic_id: 18270 reply_id: 318270[/import]