Speaking as an amateur but who has the opportunity to use various 'house PA systems' in pubs and clubs etc. I've found it is essential to be able to hear what you're singing - if you can't it is the most disconcerting thing ever.
If I can't hear myself then I politely but firmly turn down the offer of the mic. put on some heavy gauge picks and sing up!

Also the microphone "likes" some voices more than others but generally speaking most voices sound better with a little help.

If they're quiet when you're playing and applaud loudly at the end then you must be doing it right.

Mike w