Client, stakeholder or team member wants to modify scope after the scope's size or nature is signed off on.
Modification may add a delay, cost or poor quality to the project's scope. Morale among people involved will drop, furthering complexity and increasing the chance of unforeseen future issues.
Determine its importance not only to the receiver but to the work you will perform down the road. This evaluation balances importance with impact as well as affected stakeholders. If there are problems that aren't possible, don't waste time and advise at a later date. However, if these additions or modifications can be added, create potential alternatives which may also include cutting other plans or fast-tracking others.