I can't give you any specific reaction, but ATP molecules are basically what the cell uses to provide energy to where it is needed.

Because it provides energy wherever and however it is needed, for muscular contraction, for moving ions or molecules against their concentration gradients across cell membranes, for enabling energetically unfavourable reactions (pushing them uphill as it were), for moving cilia.

Each cell contains a billion ATP molecules that are being constantly used and reformed to be reused.