Pros and cons of safe oscilloscope probing methods?

[scatterandfocus]

I have seen lots of discussion around here about safe probing using either a differential probe or an isolation transformer on the device under test.  I have also seen mention elsewhere of the old school method of using 2 probes with the add function and inverting one of the channels.  It also seems that in a pinch a voltage meter could be used to check for a difference between scope ground and the ground point of interest on the device under test before probing, and simply not probing where there is a significant difference.

What are the possible issues with these various methods of probing?  For example, I saw one mention that using the scope's add function for differential probing will be noisier than using a differential probe. 

[BravoV]

An excellent application note for beginner from Tektronix on different measurements approach with an oscilloscope.

Fundamental of Floating Measurements and Isolated Input Oscilloscopes

Brief summary :

What are the Advantages & Trade-Offs for these type of measurements using the oscilloscope ?

• Isolated Input Oscilloscope
• Differential Probe
• Voltage Isolator
• "A minus B" (Two probes technique)
• "Floating" a Conventional Grounded Scope

Download link -> http://info.tek.com/rs/tektronix/images/3AW_19134_2_MR_Letter.pdf

[tggzzz]

I have seen lots of discussion around here about safe probing using either a differential probe or an isolation transformer on the device under test.  I have also seen mention elsewhere of the old school method of using 2 probes with the add function and inverting one of the channels.  It also seems that in a pinch a voltage meter could be used to check for a difference between scope ground and the ground point of interest on the device under test before probing, and simply not probing where there is a significant difference.

What are the possible issues with these various methods of probing?  For example, I saw one mention that using the scope's add function for differential probing will be noisier than using a differential probe.

Have a look at the references in https://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/