When you save back to a prior release,there are some impacts to the files.
Here are some of the limitations that affect files that are saved in prior releases. plucked from the AutoCAD 2010 help file with some edits and comments.
Saving a drawing in Release 2000/LT 2000 format is subject to the following limitations:
- File size can increase. – I did a quick test and saw my files go up from 10-20 percent when saved from 2010 back down to 2000 format. I then opened the 2000 based file and saved it as 2010 and it reduced the files size lower than the original 2010 drawing I had opened in the first place.
- Encryption and digital signatures are not preserved. – I never use these anyway.
Saving a drawing in Release 14/LT 98/LT 97 format is subject to the following limitations:
- Hyperlinks are converted to Release 14/LT 98/LT 97 attached URLs.
- Database links and freestanding labels are converted to Release 14/LT 98/LT 97 links and displayable attributes.
- Database attached labels are converted to multiline text and leader objects, and their link information is not available. Attached labels are restored if you open the drawing in AutoCAD 2000 or later.
- Dynamic block geometry can be redefined independent of the block’s dynamic elements, and the geometry in the block reference is not updated when the drawing is opened in AutoCAD 2010 or later.
- Dimensions created using the DIMARC and DIMJOGGED commands may not retain their original color in Release 14/LT 98/LT 97.
Saving a drawing in Release 12/LT 2 DXF format is subject to the following limitations: (is anyone still doing this???) (This is for DXF only – you cannot save back to DWG version 12 from inside AutoCAD 2010)
- Lightweight polylines and hatch patterns are converted to Release 12 polylines and hatch patterns.
- All solids, bodies, regions, ellipses, leaders, multilines, rays, tolerances, and xlines are converted to lines, arcs, and circles as appropriate.
- Groups, complex linetypes, OLE objects, and preview images are not displayed.
- Many objects are lost if you save a drawing as Release 12 and open it in Release 2000/LT 2000 or later. <=== keep an eye on this!
- Multiple layouts and layout names are lost. Only the Model tab and the current layout tab are saved.
- Spaces in the names of layers and other objects are converted to underscores, and their maximum length is 32 characters.
- DWF or DWFx underlay files attached to drawings cannot be saved to Release 12/LT 2 DXF format.
- The status of external references as unloaded is lost. <=== keep an eye on this!