Questions about progressive overload

1. Firstly is it necessary? obviously in the long run using heavier weights is necessary but short term, as long as you are getting tired does it matter whether you’ve overloaded?

2. More importantly, do you need to follow a plan? if i am semi regularly upping the weights on machines when i see fit does it work as well as following a proper plan or at least similarly? if a plan is important does anybody have one?

Thanks for the help!