If I absolutely need to ensure that something is properly exposed then I use a meter. If I can get next to it I much prefer to use an incident reading. If it is too far away for that then I use a spotmeter to get the reading. Otherwise I just use Sunny 16.
Please keep in mind though that I usually shoot negative film, mostly black and white, some color. Slides are entirely different. If you shoot slides you need a really good meter, otherwise you are not getting the best you can get.