It's possible that you've got bugs in an old HTML or JavaScript file, and with a cache, some users will be stuck with those old versions. This will (try to) abolish all client-side caching.

const nocache = require('nocache')
app.use(nocache())

This sets four headers, disabling a lot of browser caching:

Cache-Control: no-store, no-cache, must-revalidate, proxy-revalidate
Pragma: no-cache
Expires: 0
Surrogate-Control: no-store

Caching has performance benefits, and you lose them here. It's also possible that you'll introduce new bugs and you'll wish people had old resources cached, but that's less likely.