You can use either email or mobile no for signup process as both severs the purpose. I am listing something for you here -
Advantage of Signing Up With Email Address
1. More no of user signup for your app
2. People can try you app without giving personal information
3. user has option to leave the app they don't like without bothering thier privacy so ease for you and user both.
Disadvantage of Signing Up With Email Address
1. One user(same) can create multiple accounts with different emails.
2. More spamming is there.
3. As a user can create many account with different emails so your space and database will go waste.
Advantage of Signing Up With Mobile Number
1. One user can have only one account (more probably)
2. Chance of spamming is less
3. Your user is real and authentic as they have verified mobile no so target is good.
Disadvantage of Signing Up With Mobile Number
1. People may afraid to give a try unless they have more confidence on app.
2. Most of people don't want to give mobile no so chance is that they not try so less users.