It depends!
By this I mean, if you are a content creator, yes, by ALL MEANS install TS09. I can hear you asking why?
Well, for several reasons, in TS09 specular is much more visible then it is in TS10. I created some diesel engines recently and only looked at them in TS09 when testing. Was I getting a shock when after uploading these to the DLS I discovered the same engines were rather dull to look at in TS10. I can not be ar$ed now to retexture these with more specular and re upload these again as there was a lot of work involved to texture these in the first place. Hence I apply a bit more shine/specular now when testing objects in TS09. Then I retest in TS10 to see if that is how it should look there reasonable too.
Another reason for installing TS09 for content creators is the control of the sun/time of day/night dial in TS09's Surveyor. So bl**dy easy to use in TS09 as the tag for it is in the same right hand menu in Surveyor where engines/rolling stock, scenery, tracks, grass etc. is. In TS10 one needs to go into the top left menu to get the same bl**dy control to use. Why oh why do the powers that be shift a control from a useful location to an obscure place in Surveyor is beyond me.
I guess by the same reasoning why Micro Shaft persists in ALL window versions to have the "Rename" field right below the "Delete" field in the Window Explorer, how many countless times have people deleted something when they only wanted to rename only.
Back to TS09/10, as a content creator one NEEDS to manipulate the sun to see how an object looks from all angles when testing, hence a need for that sun/time of day tag to be easy to access.
In TS09, when using the sun/time of day dial when testing an engine or rolling stock, all all red and green direction arrows disappear, very usefull when studying a tested object close up, in TS10, these arrows do not disappear when in sun/time of day dial and stay there unless one uses (another extra click) another different tag in that menu on the right side.
Another reason is, it is much easier to get into Surveyor in TS09, in TS10 there is NO Surveyor (although references are still in the text in some descriptions there), you now have to "EDIT" a bl**dy route in TS10 instead with more clicks then just clicking on Surveyor in TS09. Not very consumer friendly, I still can't get it why some changes are necessary just from one version to another when these items before the changes where SO BL**DY EASY to use and making so much more sense in TS09 than after the change in TS10. It appears the powers that be make some changes just for changing's sake so they can say,
See, we have a new look and new outlay in the new version. Whether these changes are necessary and/or are are consumer/user friendly is another debate.
I am sure others can point out other reasons for having TS09 side by side with TS10, I sure have quite a few of reasons to do this. Especial when 2 TB hard disks are now available below the US/AU$ 100.00 mark if someone says this is taking up too much disk space.
My opinions and observations
VinnyBarb