Overheard at a dinner last week: “when you paste one presentation into the other, all the colours and fonts got mixed up, we have to deal with this all the time”.
This happens for 2 reasons:
By design: PowerPoint and Keynote offer lots and lots of designer freedom: fonts, colours, layouts, styles. Multiply even a small team x the number of things you can change in a file and there will always be differences.
PowerPoint tries to help the user by harmonising formats when Frankensteining decks together. This is actually pretty hard to do and a better user experience would have been to make preserving the original layout the default one. Usually, charts look actually pretty similar, but if 2 users use a different colour code for “blue”, disastrous things happen when your computer is going to try to sort things out for you. (You can control this behaviour in PowerPoint, see this link)
How to deal with it? Have somewhere on the corporate file server a pristine, clean PowerPoint template that will always be the starting point of any presentation. Open this one first, then paste the slides of any other deck inside it (not vice versa), and fix any mistakes you notice. In that way, you prevent the spread of template degradation as each deck is reset to its original colours all the time.
The above is one of the reasons why SlideMagic has stricter template guidelines to have you spend less time in presentation hell at the expense of slightly reduced creative freedom