Yahoo! Mail for Android is an app developed by Yahoo! Inc. to access Yahoo! Mail accounts directly from the smart phone.
There are quite some feedbacks in Android Market complaining that this app is slow, but I didn't experience any obvious slowness in my HTC Incredible S.
Despite that, I've uninstalled Yahoo! Mail because it consumed too much battery, and I couldn't find any setting to fine tune its battery consumption, such as controlling its sync behaviour.
Before I installed Yahoo! Mail, my phone will consume about 7% of battery at night during my sleep. After installed Yahoo! Mail, I noticed the battery consumption had gone to 14%, doubling up the original, and after I uninstalled it, the battery consumption now gone back to 7% during sleep again.
Looks like Yahoo! need to pay more attention to their QA before releasing the app.