A non-all-in in RTS would try to hit the opponent’s economy. Going for the workers is pretty rare in Codex, the equivalent would be destroying their tech buildings to stop them bringing in powerful units / more heroes. Conversely, you’re going all-in if you focus on attacking the base directly, instead of controlling the game by destroying the tech buildings.
Red is probably the colour that excels the most at doing this early – my favourite recent example is here – but everyone can have reason to do it, even if you don’t plan for it in advance. For example, you might have a good presence on the board, but have your tech buildings destroyed, or have drawn into a really bad hand, or are using a strategy that trades gold efficiency for strong, immediate board presence. If the game lasts much longer, you’re in trouble. So, you go for the base. (Insert obligatory Day9 clip here.)