Deciding whether a volunteer plant is worth keeping in a crowded bed

A volunteer squash plant appeared in the vegetable bed and is growing enthusiastically. I didn't plan for it, and its leaves are already shading herbs nearby. Part of me wants to let the surprise develop; the practical side says it will swallow the space. How do you decide whether an unplanned plant earns a spot in a crowded garden? I'm tempted to give it one corner and prune aggressively.