In addition to focal reduction (thereby widening the field of view) reducers have a few pros.
They widen the Field of View (FOV) and shorten exposure times. For example, my EdgeHD at native focal length (2032mm) is f10 (means longer exposures and more accurate guiding is required.) Longer FL/narrower FOV means you need better guiding which means a better mount, guider/OAG, etc. More gear = more weight = bigger mount to keep everything stable...it's a ripple effect.
With the 0.7 reducer the FL shortens (1422mm) and f7 means slightly shorter/faster exposures. The shorter FL means a wider FOV. It also means slightly improved guiding since the wider FOV adds more stars to the OAG's FOV.
The cost, besides $$ for the reducer, is that you lose some resolution when shooting planets and galaxies. It also shortens your back focus which could make spacers, focusers, OAG, filter wheels, etc. more complicated. You may have to get a longer plate/dovetail to push your OTA, and all that stuff hanging off the back of it, further over/forward on your mount.
For my setup (OTA, mount, etc.) and the targets I wanted to shoot (narrowband DSOs and selected galaxies), the 0.7 reducer had more pros than cons.
Edited by SoDaKAstroNut, 23 May 2020 - 04:41 PM.