Here's some info that you may find helpful.
In general:
When pasting text using the keep text only setting, the pasted text will be in the style in effect at the cursor position. Keep text only is, roughly, the same as
keep destination style in W2003.
When pasting text using the keep source formatting setting, the underlying style of the pasted text will be in the style in effect at the cursor, but it will have direct formatting that matches the direct and indirect formatting of the source.
You see that this is the case by selecting the pasted text and pressing Ctrl+Spacebar, which clears the direct formatting and reveals the underlying style.
When pasting using the merge formatting setting, the pasted text will be in the style in effect at the cursor and be clear of direct formatting except for places where there is direct formatting in the source. This retains direct formatting that
may be meaningful, such as italics (when used to indicate publication titles for example) super- and subscripts, and bold.
The last choice was new with, I think, W2007, and for documents that have meaningful direct formatting, is the most useful paste option.
We no longer need the convenience of a paste text only macro and keyboard shortcut because placing the cursor where you want to insert copied material and right clicking displays a flyout menu (in W2013) or paste option bar (in W2010, I think) with all the
options.
I leave the advanced cut and paste options at the defaults and either use, out of habit, my paste text macro or click the paste option I want.
HTH,
Pam