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The low thermal expansion/contraction of a carbon fibre tube or trusses can assist with astrophotography, but I personally think much of this is hype. Manufactures claim that carbon fibre tubes/trusses can reduce the amount of times you need to refocus during an astrophotography session. This statement depends on the size of the critical focus zone.
Generally, the faster the optical design (f-ratio), the smaller the critical focus zone (in microns). So if your OTA shrinks or expands due to temperature changes through the night by 100 microns or so and you're using a fast optical system you'd need to check focus regularly. But in all seriousness I've never come across this. More importantly, who doesn’t recheck focus after a few exposures or change of a colour filter? I know I do.
If anything I think the carbon fibre benefits are strength and weight, compared to maintaining critical focus.
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