I put the Windows install date on up top on the info tab in D7 because I like to know when the last clean install was done (although repair installs reset this...) because occasionally I have a system with a LOT of issues, then I look at that and think, man, it's time to N&P this thing, it's old!
Sometimes there could be tons of little issues with a system you don't need to waste hours tracking down and fixing all of them when you can do it in far less time. This either saves your customers money, or it saves your wasted efforts and you make much more per hour of teching than you would otherwise, or both.
Now as a tech I'm inclined to take the hard road and track down all the issues, because I don't think in terms of business I think in terms of "hey there's a problem, I'm gonna fix it if I'm worth my salt."
But I try really hard to think of what works out best for the customer AND for my company, in the given situation. Sometimes the customer really would be happier with an N&P if they've had numerous issues with their current install - or have issues they forget to tell you about. Things you don't check for in the course of a typical repair. If the customer is happier, then your business is better for it.
But it's all about keeping them happy. I have one client with an XP install dating back to 2002 or 2003 I believe. PC has been upgraded numerous times. He has had countless infections over the years, and tons of other problems. I quit working for the place he was a customer of, moved to another city, years later moved back, now working for the same employer again he is my client again -- still the same XP install. And this guy loves crappy registry cleaners and system performance increasing apps and all that total BS people buy into, no matter how hard we explain they either don't work or cause other issues... and there are so many quirky things about this install that just aren't right. For instance in add/remove programs, the list gets broken up by thousands of lines of blank and solid black lines, so you've got to scroll forever to find something in there. No harm no foul, so we leave it alone... but tons of quirky little issues like that all resulting no doubt from years of corrupted registry replacements and those crappy apps he likes so much.
As a tech I've spent tons of hours on that guy's computer, and it's always challenging. If there ever was a problem with XP, this guy had it more than once. But as much as I want to N&P a 10 year old Windows install just on general principal, he pays to keep that thing running just the way it is. At least he pays. If he didn't, then he'd either get an N&P one day whether he liked it or not, or I would just turn his business away.
I'm beginning to think we should close duplicate threads...
