I replace things when they no longer meet my needs. This might be because it's worn out, or just because my needs have changed. For example, I kept my first sewing machine for over 20 years. I thought I would keep the second one just as long, but it turned out that after 3 years I wanted a bigger throat space, so I upgraded.
I give away items that don't meet my needs, but are still workable (for example, I like trying out rotary cutters, but I give away the ones that aren't my favourites). I've got another 20+ years in the workforce ahead of me, so right now I have more money than time. I'm not going to waste time using a rotary cutter blade that skips, when I can replace it and get on with my cutting. My jar for dull or bent pins sits next to my pin dish. Basically, as soon as something turns my fun into a chore, it's outta here.