That's important and should be implemented if it is technically possible.
Because entering the login and password over and over again in different sites is a hassle!!!
You do it once in a while, it is ok
You have to do it again 5 times, if you visit that site 5 times in a day, that's a real burden!!!!
Smooth up the experience - Make it easy AND enjoyable for your members to come back over and over again.
What's the ideal?
Keep them logged in for:
- 1 month?
- 3 months?
- 6 months?