Flattening images in PS

When I work on images in PS I usually end up with several layers. I never flatten these layers but on some occasions I might merge down where necessary.
Lots of tutorials I have followed seem to recommend flattening layers and I don't see why because once flattened it cannot be unflattened without a lot of work.
Is there any benefit in the image quality for either printing or converting to jpeg by flattening?.
I will appreciate your comments.
John Moore

Hi John,

As far as I am aware the only advantage is disc space and computer speed. The smaller file size will load quicker and transfer to your printer quicker. I normally keep two copies on separate drives for safety, one copy with all the layers and one copy flattened ready to print. If you are going make a jpeg copy then it will be flattened automatically as soon as you Save As a jpeg.
Another benefit of the smaller file is that some library and sorting software eg ACDSee cannot always open the large files.
Hope this helps.

David Lowe
www.davidlowepics.com

Thanks david, that seem to make sense.
Thanks for your feedback.
John