Clever word play for a title might inspire a plot. An emotional scene might make me eager to build a story around it. A dynamic character could be an interesting inclusion in a half-finished manuscript. The problem is my mind is bombarded with ideas everyday!
A writer must be selective about which ideas to pursue, for the hours in the day are limited. I choose the ideas that win my heart and stick with it. If a project was pushed aside every time a new idea popped up, none of my manuscripts would ever be completed. Often, these ideas can be added in a work-in-progress, but not all the time. There must be a limitation or a manuscript will become littered and overworked.
Of course, several of those ideas plaguing my mind could be of use later on. What I do is keep a journal filled with bullet points and tabs, but it acts as a reference if I require inspiration or a new project. Keeping this journal allows for past ideas to compete for my heart. And who knows? I might actually fall back in love with old inspiration.