You should replace it as often as you can. But as a limit, do not keep a sponge for more than a month. I do not see myself using a couple of sponges a week, so what I personally do is change my sponge every 15th and every 30th of every month.
Bathtub Refinishing, Ceramic Tile resurfacing, Countertop & Cabinet ... When bathtubs start to show their age, owners are often tempted to replace them altogether. ... Beautiful Finishes can refinish kitchen countertops and bathroom counters ..
Every day
Changing your kitchen plumbing is not a safety issue. Your pumbing should be changed only if they need it.
Not often if there tarting to wear and tear you should replace them.
on a regular basis
Kitchen hood vent cleaning should be performed at least every six months to ensure optimal performance and safety in the kitchen.
How often should you change water pump in a boat
Replace headlight bulb only when blown.
Take apart and change washer, or just replace entire faucet set, often easier.
I've heard you should replace your pillow when you can bend it in half without it bending back.
Normally minimum wage if they are lucky, Kitchen porter jobs should be seen as way into a commercial kitchen, the jobs are unskilled and often dirty, but they give you an insight in the workings of a kitchen.
all the time