A few questions about my new Canonet QL-17 GIII

[Dawid]

It will reduce both grain and sharpness on C-41 films, but on conventional B&W negative films it will often increase grain.

That's the price you pay for shooting street with a camera without light meter or automatic modes. If you have to shoot fast, there may be no time to use handheld meter. When that happens, it is better to overexpose than underexpose.

Of course, while shooting landscapes or portraits, to get the best result possible, proper exposure is essential. 🙂

Use what you prefer, there is no reason to shoot manual just because other people might. There is no 'best', use what you prefer and what works for you.

Absolutely agree. 😉