The Dutch imperfectum (simple past) and perfectum (present perfect) are not about formality or casual versus formal speech. The main difference is that perfectum is used for completed actions with relevance to the present, while imperfectum describes ongoing or repeated past actions, or sets the scene. There is no direct parallel to English where one is more informal; both are used in everyday speech and writing, depending on the context.

Here is the practical breakdown. Use the perfectum when you talk about a single, completed action in the past that has a result or connection to now. For example: 'Ik heb gisteren een boek gelezen' (I read a book yesterday). The focus is on the fact that it is done. Use the imperfectum when you describe a past situation, a habit, or a sequence of events without a strong link to the present. For example: 'Toen ik jong was, las ik elke dag' (When I was young, I read every day). The imperfectum sets the background or tells a story.

A common tradeoff: beginners often overuse the perfectum because it feels safer with its helper verbs. But to sound natural, you need both. The imperfectum is especially important for storytelling and for using modal verbs like 'kunnen', 'moeten', 'willen' in the past (e.g., 'ik kon', 'ik moest'). If you only use the perfectum, your Dutch will sound like a list of facts rather than a narrative.

As for emphasis: no, the perfectum is not used for emphasis like in English. In English you might say 'I have done it!' to stress completion. In Dutch, emphasis comes from word order or adding words like 'wel' or 'toch', not from switching tenses.

Should you save your breath and stick with the imperfectum? No. That would make your Dutch sound unnatural and limited. Instead, learn both as complementary tools. A good next step is to practice describing your weekend in both tenses: first using perfectum for each separate event, then retelling it as a story using imperfectum. Notice how the meaning shifts.

A simple rule to start: if the action is a single event and you can add 'just now' or 'already', use perfectum. If you are describing a scene or a repeated action, use imperfectum. Over time, exposure to native speech will make the choice intuitive.