I am editing both in-house and client sites and working live. Editing complex ASP functions is not a problem if you know what you are doing. If in doubt I create a duplicate of the page until it tests ok.
I also have sites on Linux servers and find it too tedious to work locally and then upload, that's if the design/layout is already established, in which I use the file manager in Webmin and edit the html onsite.
Either way there is no great danger as straight away you can see if it works or not and within 10-15 seconds undo what you did or correct it.