Makus, thanks for your first guest post. Please consider registering here.

Regarding to your question, well like everything in life it depends on much factors. I write my example:

When I purchased my bike, it came with a compact crankset 50-34 and a cassette of 12-23. It was good but not great for triathlons. I needed a smaller cog of 11, so I replaced it by 11-23. Now I've got the perfect cogs distribution for training uphills with 34-25 and racing with 50 – x.

PS. I'm thinking on replacing it by 11-28 because I'll be doing a lot of hill training.

It depends ;) makus