pros and cons of various image file formats:
http://www.photoshare.org/phototips/digital101.php
bottom line: use the format that fits the purpose, ie better in the sense that it is better suited for its intended use.
PSD is specially designed for image processing done on Photoshop and should be the ideal format if you want to store all your editing data and processes.
TIFF is just a lossless image format like BMP or GIF. TIFF may be able to store layers but it was not designed to store image processing workflow data.
But of course if you want to post your pic for display or print, by all means convert it to TIFF or JPEG and not post it as PSD!
In my work flow, starting from RAW, the developed picture will be saved losslessly in TIFF, and the editing will be saved as PSD, in which I can save several output versions, eg B&W, alternate processing, with/without effects, etc, and then the final output which can in turned be saved in several flat files, ie without layers, depending on display media, eg for web 72dpi, reduced sized JPG, for paper print, 300dpi TIFF, resized according to paper size, etc. Each of these output formats will be generated from the PSD, each time there is such a need.