I believe that this is very personal business and individual.
So, my answer is: yes, it's worthwhile to send individual welcome letter. Depends when he became your PSA, when he/she join.
I usually send my Team emails Sunday, but if my new PSA came Monday, of course that I will send him new, welcome letter and follow his baby steps in SFI Journey.
I hope this is going to be useful.
Wish you all the best!
See you on the top!
