If your technical illustrations are in Adobe Illustrator format and you wish to convert these to CGM, there are a couple of things you should take into consideration.

Adobe Illustrator uses the Bézier path to describe vector graphics. Everything from a single line to a circle or curve ends up as a Bézier path in an Adobe Illustrator file.

Drawing extent:
It can happen that an .ai file contains graphic primitives outside of the border around the actual illustration.
When converted to CGM, these elements will be converted as well. This increases the file size. It also influences the extent of the illustration. If a CGM file is used "shrink to fit" in an SGML or HTML environment these elements will cause additional unwanted scaling to happen.

Recommendation: 
No graphic primitives should be allowed outside the frame delimiting the illustration. Primitives that intersect the frame should be cut so that no portion remains on the outer side of the frame. It is not sufficient to cover these elements with a white area.

Vectorized Text:
An .ai file can contain text that had been converted to outlines. This prohibits the automatic generation of hotspots on vector text elements.

Recommendation:  
Disallow outline text in cases where text will be used as a hotspot.

Overlapping Elements:
A popular drawing technique used by Adobe Illustrator users is to cover up unwanted elements with filled areas. In most cases this is done because it is less work than to actually cut the elements underneath. The file sizes increase considerably due to these invisible elements.

This becomes very important in online documentation, because the invisible elements will have to be read and rendered every time the file is opened and redrawn on a screen - even if at the end the elements stay invisible.
 
Recommendation: 
Covering primitives with white areas should be restricted as much as possible for performance and complexity reasons.

Colors:
Most CGM profiles do not know the concepts of gradient fills (interpolated interior fill). As a consequence, these gradient fills will have to be converted into simpler shapes like groups of Bézier paths where each path has a slightly different fill color.

Typically between 50 and 255 Bézier paths are used to approximate such a gradient fill. This leads to heavily increased file sizes in CGM. Another side effect of this is that the resulting CGM files contain large quantities of Bézier paths. This may lead to problems with some CGM applications that do not support Bézier paths very well.

Recommendation:
Use plain colors instead of gradient fills.