giving google your mobile number
 

Hi guys,
google frequently asks for giving a mobile number 'just in case'
have you guys given it? and do you advise on giving it?

also: what email service do you use?

I use Gmail but I don't give my mobile number when they ask for it. I don't know if it's advisable or not but I don't feel comfortable about doing it.

It's for password protection/recovery purposes. Search for two-step verification google.

If you're not comfortable giving it out and don't want two-step verification, don't give it out. Google isn't going to call you, but you also don't have to give out your number to use Google services.