Standard for figure description in main text and its placement in a report/paper
The following applies:


Figures should appear at the first possible place after they are referenced in the text and thus also in the order they are referenceed in the text. (the physical placement of the figure follows typographical rules). 
A figure may be placed before its reference if they are on the same page. Figures are normally place at the top of pages.
Figures must be ordered according to the order in which they are first referenced.
The same system also applies for tables. It is however, not necessary for figures and tables to be placed in the order they appear relative to each other, they are two independent series of inclusions and placement depends on typographiccal rules.


The logic is that the order figures are needed in the text also determines their location. Having such a rule makes the location predictable. Thse rules are followed by all journals typeset by professionals.

The case of the figures is dealt with as follows. If a figure has two panes, they would count as one figures but be labelled (a) and (b). thus one can reference figure Xa in one place and figure Xb in another. Combining panes into larger figures is a way to save space but most importantly to group plots that relate to each other in one place. ths is one way in which the order of figures according to the list above can be circumvented. 

The important aspect is that figures should make sense and provide the reader with as much information as possible. Placement is done according to a logical and predicatable rule so that we all know what to expect.