Back on the original topic:-
As per the original query I don't personally have an issue keeping or referencing stuff I personally worked on, be it example project calculations, reference drawings, personal spreadsheets developed on company time for specific purposes, etc. Certainly our local professional licencing requires you to maintain evidence of past work practice for the purposes of 4-6 yearly reviews on your Chartered Professional Engineer status, and you can quite easily have a number of employers during that time and sourcing these examples after the fact can be quite challenging.
I wouldn't/don't keep stuff by others like company spreadsheets (etc), but main reason is they usually have a high percentage chance of containing errors and/or I cannot follow how they work and there is very little in the way of formal verification (basically no one knows who wrote them, and I don't fully trust them without taking them for a serious test drive to determine if they are in fact a well oiled machine or an old rust bucket). This is as opposed to this stance being primarily a question of maintaining/respecting a firms IP. Most stuff like this is better to recreate yourself from the same principles so you understand how it works (and hopefully discover all the errors others made).
Drawings & specifications/calculations unless confidential are in the public domain and are easily sourced from local authorities in this part of the world, so any member of the public can effectively obtain them.
Previous employers have benefited from the tools/templates I have created, to some degree these things were produced on my own time and were produced for my own personal use in the first instance. I simply let them use them and I left jobs with the terms that I would no longer support them after I was gone but they could continue to use them and develop them further if they so desired. I'm sure the law would say it then belongs to them, but I've always thought if it comes to it they are welcome to pay me for all the free time I have poured into the development of these things for my own use if you are saying you own them.
I have had people who left my previous employer turn up with my own personal spreadsheets and use them at another employer, much to the disgust of my employer at the time as they felt it gave them an advantage compared to their competitors. Initially I was ok with the fact that others were using these things, but considering some of the effort (hundred of hours) that went into some of my own tools and the fact that I was sometimes finding and correcting errors which they would not subsequently benefit from, I have since changed my mind on this aspect (liability comes into it, and also the older it gets it just pisses me off when someone I didn't respect walks off with my hard work). I have since this event taken active measures to protect my spreadsheets (they will not function unless certain parameters that are unique to a company network are present plus a whole raft of other protection measures to prevent/minimise reuse or adaption outside of my current employers environment).
I've also seen some of the companies I have peer reviewed designs for turn up with identical spreadsheets/CAD templates from other companies, because some guy left to form a new company and appear to have taken everything with them as a starting point.
I've also heard of one local architectural company that went after another local company for IP theft related to the use of the architectural companies Revit template (supposedly gained when an employee jumped ship).
