I replace them as it becomes necessary. When pins are bent, needles dull, rotary blades when dull, rulers when the corners are rounded, markings worn off, cracked--, seam rippers when dull or bent, cutting mats when worn out ( I've replaced my big one once in 16 years, about 7 years ago. I think it stil has many years to go.) scissors, machines-- I've never replaced. I have one pair of my grandmothers scissors that are sharp- great scissors! ( she passed away 30 years ago-- I bet they are at least 60 years old. Buy quality tools and take care of them they should last a life time-- or many lifetimes. I have a 1956 machine that sews beautifully, my Viking is 16 years old-- equipment if quality to start with lasts too. All of my rotary cutters are all 15+ years old, I've never replaced one--my first one is still my favorite, the one I'm most comfortable with. I have many though-- different sizes, shapes; some were gifts, or prizes.
Chairs-- I've switched sewing tables & chairs a few times over the years, moves, rearranging space, trying to find the best chair for the task. I try to take care of all my tools & equipment so I don't have to replace them. I did upgrade my Longarm 3 years ago. I'd had the old basic one for 12 years-- it was time for an upgrade.