whats the purpose of this? just fun or does it cause some desired behaviour?
Fun is desirable.
Except for software gigs the software typically belongs to the customer so you'd need to rewrite it every time...
And contractually, any code I made was my employer's if I made it during office hours. Some even made a claim for code I would've written that during my employ that would be "competitive". Luckily, there was a massive difference in what I would do in my own time versus what they did.
When I'm hired in a company (not contract), they wipe the harddrive when I leave (well, I also do it before I hand it over sometimes). So they don't get the tools (I take them with myself, it would be a waste to loose them)
Some agencies do, however; it's dependent on the contract specifics.
for me, it’s not about the cost to leave, it’s about lowering the cost of onboarding and change.