Support team would prefer seeing Cases module first thing when they login and Sales Team would prefer landing into Opportunities module as soon as they enter Vtiger.
To setup the default module which you will be redirected to everytime you login to Vtiger, please follow the below steps:
1. Click on your User icon
on the right top corner
2. Click on My Preferences
3. Scroll down to the Vtiger Usage Preferences
4. Select the desired module under Default page after login
Refer : My Preferences