Yes - it's important to ensure that files are under their required maximum.
In order to allow the Kindle download option, your files must be no larger than as follows:
24MB for PDF
24MB for MOBI
16MB for EPUB (we convert to MOBI from EPUB and this adds data)
For downloads to all other devices or apps, our files must be no larger than as follows:
NetGalley's official file size maximum is 40MB, but we can successfully create Adobe-DRM versions of the files that are twice that size (~80MB). Beyond 80MB or so, the conversion process fails.
The official file size maximum is capped much lower because we've found that larger files often result in a lower quality experience for our members. Larger files are less likely to be well-supported by all reading devices, and are more likely to cause those devices to freeze. Our goal is always to provide a consistently positive reading experience for our members. As the average capacity of reading devices increases and they improve overall though, we are happy to re-evaluate this file size maximum.