Good idea to transfer all phone numbers from SIM card to google contacts? I am new to the whole smartphone thing. Currently all of my telephone contacts are on my SIM card. I suspect it makes sense to move all my phone numbers from the SIM card to my Google contacts (i.e. adding the numbers to existing Google contacts who mainly contain only email addresses). The benefits would be: (a) no more duplicate contacts in my list, (b) automated backup of my contact's phone numbers.

Or, is there something I should be aware of before I do this effort? Will there be some workflow side effects? (apart from not having my contacts on SIM anymore)

Edit: I just transferred all. Actually, I did not remove the contacts from my SIM card, I just hid them using the contacts settings. So if I ever have to use my old phone as a backup, I'll have most of my phone numbers in there
I'm not going to answer if it's a good idea or not - you need to solve that for yourself :).

Having your contacts stored with Google Contacts will eliminate any duplicates (at least duplicates where you have the number stored in the SIM and e-mail in Google, or something like that) and allow you to manage/sync those contacts from anywhere you can access Google Contacts, like a computer.  You are correct that it will 'backup' your contacts so that if you were to switch phones or even carriers, you wouldn't have to worry about bringing your contacts as long as the phone you have supports Google Contacts (web or app).

Keeping your contacts on the SIM allows you to keep them from Google (if you're worried about privacy), and if you get another SIM-based phone, you can easily move them (provided you keep the same SIM).

Personally, having my contacts in Google Contacts has been great.  Easy synchronization, use photos from Picasa as contact photos, management from a computer... but you will have to decide for yourself which is "better".

You may want to see this answer to help you move your contacts from the SIM to Google Contacts.